Raspberry Pi Email Server Part 2: Dovecot

Dovecot Logo

This is the second part of a five part tutorial that will show you how to install a full featured email server on your Raspberry Pi. This tutorial covers Dovecot, which provides SASL authentication and IMAP capabilities. The parts are:

The Introduction & Contents Page (read first)
Raspberry Pi Email Server Part 1: Postfix
Raspberry Pi Email Server Part 2: Dovecot
Raspberry Pi Email Server Part 3: Squirrelmail
Raspberry Pi Email Server Part 4: Spam Detection with Spamassassin
Raspberry Pi Email Server Part 5: Spam Sorting with LMTP & Sieve

Fixing the errors that appeared during dovecot installation

In part 1, when you installed Dovecot I mentioned that you might see some errors like this:

Creating config file /etc/dovecot/conf.d/20-imap.conf with new version
[....] Restarting IMAP/POP3 mail server: dovecotError: socket() failed: Address family not supported by protocol
Error: service(imap-login): listen(::, 143) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(imap-login): listen(::, 993) failed: Address family not supported by protocol
Fatal: Failed to start listeners
 failed!
invoke-rc.d: initscript dovecot, action "restart" failed.
dpkg: error processing dovecot-imapd (--configure):
 subprocess installed post-installation script returned error exit status 1
Setting up dovecot-ldap (1:2.1.7-7) ...

These errors are caused by the lack of IPv6 support, which I mentioned in the previous tutorial. To remove the errors, open the main dovecot configuration file (/etc/dovecot/dovecot.conf) and find this line:

listen = *, ::

And change it to:

listen = *

The * means “all IPv4 addresses”, the :: means “all IPv6 addresses”. Now restart Dovecot, and you shouldn’t get any errors:

sudo service dovecot restart

Note: since I wrote this tutorial, there have been a few small changes to the default configuration file - you may find that the line is commented (with a # at the start of the line). If so, remember to uncomment it when you make your changes!

Tell Dovecot where your Mailbox is

Open /etc/dovecot/conf.d/10-mail.conf and find this line:

mail_location = mbox:~/mail:INBOX=/var/mail/%u

Change it to this:

mail_location = maildir:~/Maildir

Instruct Postfix to use Dovecot SASL

Now we need to tell Postfix that we would like to use Dovecot for SASL authentication. Open /etc/postfix/main.cf and add these lines:

smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes

Now tell Dovecot to listen for SASL authentication requests from Postfix. Open /etc/dovecot/conf.d/10-master.conf and comment out the current block that begins with service auth (place a # at the start of each line). Replace it with this:

service auth {
        unix_listener /var/spool/postfix/private/auth {
                mode = 0660
                user = postfix
                group = postfix
        }
}

Now you want to enable plain text logins. Do it by adding these two lines to /etc/dovecot/conf.d/10-auth.conf. Make sure they are not already present in the file, or your settings may be overwritten with the default ones if the default is declared later in the file than the lines you add. If the parameters are already present, you can either modify the existing lines or comment them out and add these new ones:

disable_plaintext_auth = no
auth_mechanisms = plain login

Note that although the logins are in plain text, we will be setting Postfix up later so that it only allows you to use plaintext logins from within SSL/TLS. This means that your login and password will sent in an encrypted session - you wouldn't see them in plain text if you used a packet sniffer, for example. For now, we’re allowing unencrypted plain text logins so that we can test logging in with Telnet. Since the connection is local (from the Pi to the Pi), your password isn’t being sent over any insecure networks so this is fine.

Testing SASL

Creating a new user for testing purposes is a good idea. Let’s call this temporary user testmail and give it the password test1234 Use this command to add the user, and follow the prompts including setting a password.

sudo adduser testmail

Now restart Postfix and Dovecot:

sudo service postfix restart
sudo service dovecot restart

We’re now going to try and send an email after authenticating with SASL. The server is expecting to see a base64 encoded version of your username and password, so we have to convert it first. There are three ways of doing this, so I've given examples below using the testmail username and test1234 password:

#Method No.1
echo -ne '\000testmail\000test1234' | openssl base64

#Method No.2
perl -MMIME::Base64 -e 'print encode_base64("\0testmail\0test1234");'

#Method No.3
printf '\0%s\0%s' 'testmail' 'test1234' | openssl base64

I have discovered that if your password starts with a number, methods 1 and 2 don’t work. Assuming the username and password are testmail and test1234, the commands produce this:

AHRlc3RtYWlsAHRlc3QxMjM0

WARNING: If you’re having problems with authentication and you paste examples to forums or mailing lists, be aware that it is really easy to convert this back into your username and password (hence the creation of a test user). If you're using your real username and password to test, redact it before posting!

Now, still logged into the Pi via SSH, you can telnet port 25 to test whether or not SASL is working. There’s only one extra step, which is the AUTH PLAIN command that comes after ehlo but before mail from. For testing, the permit_mynetworks parameter should be commented out under your postfix smtpd_recipient_restrictions block in /etc/postfix/main.cf. If you’re following on from Raspberry Pi Email Server Part 1: Postfix then this should already be the case. If you have to change it, remember to reload postfix (sudo service postfix reload) after you change the value. Here’s an example:

telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 samhobbs ESMTP Postfix (Debian/GNU)
ehlo facebook.com
250-samhobbs
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
AUTH PLAIN AHRlc3RtYWlsAHRlc3QxMjM0
235 2.7.0 Authentication successful
mail from:testmail
250 2.1.0 Ok
rcpt to:me@externalemail.com
250 2.1.5 Ok
data
354 End data with .
Subject: This is my first email that has been authenticated with Dovecot SASL
Woop woop
.
250 2.0.0 Ok: queued as B87133F768
quit
221 2.0.0 Bye
Connection closed by foreign host.

Now try again but enter the username/password incorrectly (base64 encode something random) – you should get an error message and the email won’t send. If everything went to plan, then SASL is working properly!

You can now uncomment permit_mynetworks again.

Separating Incoming email (unauthenticated) from Outgoing Email (SASL authenticated)

It’s probably a good idea to have a dedicated port for sending outgoing email…here’s why: Port 25 doesn’t require (but does offer) SSL/TLS encryption. If you mess up configuring your mail client you could end up letting it authenticate with SASL over insecure connections. Using a different port that only accepts SSL/TLS connections removes the risk that a poorly configured email client could be sending your password unencrypted over dodgy networks. There are two ports you can use for this:

  1. 465: SMTP over SSL
  2. 587: Email submission

587 is the “official” port for email clients (like K9 mail, Thunderbird and Outlook) to use when submitting messages to the Mail Submission Agent (your email server) – the submission may be encrypted or unencrypted depending on the server configuration. 465 was a port that was assigned for SMTP with SSL/TLS before the STARTTLS protocol was introduced, back in the days when you chose your port and that decided on the type of connection you were going to get (encrypted or unencrypted).

STARTTLS changed things because it allows you to connect with an unencrypted connection (like the one you get with Telnet), and then upgrade to an encrypted connection without changing port… so when STARTTLS was introduced, SMTPS on port 465 was removed from the standard because you could do the same thing with a single port (25).

However, I think there is some value in specifying a port for submission that only accepts SSL/TLS encrypted connections, and won’t work if the connection isn’t encrypted. This means that if you misconfigure your email client it just won’t work, instead of working and sending your password in an unencrypted format. So, anyway… Here’s how to set up Postfix to listen on port 465 for encrypted connections. The first step is telling Postfix to listen on port 465, so open /etc/postfix/master.cf and uncomment the line:

smtps     inet  n       -       -       -       -       smtpd

Now restart Postfix:

sudo service postfix restart

Test whether Postfix is listening on port 465:

telnet localhost 465
Trying 127.0.0.1...                                                                           
Connected to localhost.                                                                       
Escape character is '^]'.
220 samhobbs.co.uk ESMTP Postfix (Debian/GNU)
ehlo samhobbs.co.uk
250-samhobbs
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
quit
221 2.0.0 Bye
Connection closed by foreign host.

OK, so now it’s listening on the right port, but it’s allowing unencrypted connections. Here’s how you force TLS on port 465: open /etc/postfix/master.cf and find the line you uncommented earlier. Below it are some options, you want to edit them so that they look like this (i.e. uncomment lines 2 and 3):

smtps     inet  n       -       -       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes

Line 3 is forcing TLS on port 465, and line 2 means that connections to port 465 have a different label in the logs, which can be useful for debugging.

sudo service postfix restart

Now try connecting with Telnet again… you should be able to establish a connection, but not receive any prompts from the server:

telnet localhost 465                                            
Trying 127.0.0.1...                                                                           
Connected to localhost.
Escape character is '^]'.
exit
exit
Connection closed by foreign host.

Now try openssl:

openssl s_client -connect localhost:465 -quiet
depth=0 CN = samhobbs
verify error:num=18:self signed certificate
verify return:1
depth=0 CN = samhobbs
verify return:1
220 samhobbs.co.uk ESMTP Postfix (Debian/GNU)
quit
221 2.0.0 Bye

Good: we are able to start a TLS encrypted connection. We got some errors because the certificate is self-signed (it's not signed by a certificate that is in the trusted root store on the server) but this is OK because we're just using the certificate for testing for now. When you come back later to set up a proper certificate, you can use this command to verify it. The -CApath option tells openssl where the trusted certificates are stored on your system:

openssl s_client -connect localhost:465 -quiet -CApath /etc/ssl/certs

Successful validation looks something like this:

sam@samhobbs:~$ openssl s_client -connect localhost:465 -quiet -CApath /etc/ssl/certs
depth=3 C = SE, O = AddTrust AB, OU = AddTrust External TTP Network, CN = AddTrust External CA Root
verify return:1                                                                              
depth=2 C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = COMODO RSA Certification Authority
verify return:1                                                                              
depth=1 C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = COMODO RSA Domain Validation Secure Server CA
verify return:1                                                                              
depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = samhobbs.co.uk                 
verify return:1                                                                              
220 samhobbs.co.uk ESMTP Postfix (Ubuntu)                                                    
quit                                                                                         
221 2.0.0 Bye

There are a couple more changes we want to make here: first, tell Postfix to only advertise SASL authentication over encrypted connections (so that you don’t accidentally send your password in the clear). Open /etc/postfix/main.cf and add this line:

smtpd_tls_auth_only = yes
sudo service postfix reload

Now connect to port 25 and you shouldn’t see AUTH advertised:

telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 samhobbs.co.uk ESMTP Postfix (Debian/GNU)
ehlo samhobbs.co.uk
250-samhobbs.co.uk
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN

Lastly, we want to override the smtp_recipient_restrictions for port 465 so that it doesn't accept incoming messages from unauthenticated users.

At first, I didn't make this change and I noticed that some spam emails were coming in on port 465 and bypassing my spam filter, which I configured to scan all incoming email on port 25, but not 465 because I only expected it to be used for outgoing email. We can do this by overriding the smtp_recipient_restrictions list for port 465 in /etc/postfix/master.cf. Open master.cf and find the smtps line. Add a new recipient restrictions list option like this:

smtps     inet  n       -       -       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject

Now reload postfix:

sudo service postfix reload

Perfect! Postfix configuration is now complete.

Testing IMAP

There are two main protocols for fetching mail: POP and IMAP. The main difference between them is what they do with emails when they collect them: a POP client will fetch email from your server and remove it from the server when it’s done. This is inconvenient if you want to connect with two or more devices (like a phone and a computer) and have complete copies of all your emails on both. IMAP, on the other hand, makes a copy of the emails on the server and leaves the originals there. For this reason, I think IMAP is much more useful than POP and I didn’t even bother to set up POP on my server. We can now test the IMAP server with Telnet in a similar way to SMTP & SASL testing earlier. This time, we’ll be using port 143, the standard port for IMAP. The stages are:

  1. establish a connection with telnet localhost 143
  2. log in with a login "USERNAME" "PASSWORD"" (not base64 encoded this time)
  3. select inbox to see messages inside b select inbox
  4. logout with c logout

In case you're wondering, the "a b c" thing is done because a client can send multiple commands to the server at once, and they might not come back in the same order depending on what they are. So, the responses have the same letter as the commands they are responding to so that the client doesn't get muddled.

Here’s an example, using the testmail user we created earlier:

telnet localhost 143
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
a login "testmail" "test1234"
a OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE] Logged in
b select inbox
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permitted.
* 1 EXISTS
* 0 RECENT
* OK [UNSEEN 1] First unseen.
* OK [UIDVALIDITY 1385217480] UIDs valid
* OK [UIDNEXT 2] Predicted next UID
* OK [NOMODSEQ] No permanent modsequences
b OK [READ-WRITE] Select completed.
c logout
* BYE Logging out
c OK Logout completed.
Connection closed by foreign host.

Adding TLS support

Now that we know IMAP is working, we need to enable IMAPS (imap with SSL/TLS). The standard port for this is 993.

Many other tutorials that were written for older versions of dovecot will tell you to do this in different ways that won’t work, I tried 3 different methods before I ended up with a working one.

First, edit /etc/dovecot/conf.d/10-master.conf, find the “service imap-login” block and uncomment the port and SSL lines so that it looks like this:

service imap-login {
  inet_listener imap {
    port = 143
  } 
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}

Edit 14/10/2015: the default dovecot configuration files changed recently after Jessie became the new stable distribution of Debian, which caused some users problems; TLS on port 993 used to be enabled by default but now it isn't. We need to re-enable it.

In /etc/dovecot/conf.d/10-ssl.conf, find ssl = no and change it to:

ssl = yes

There have been some security vulnerabilities discovered in older versions of the SSL protocol in recent times. SSLv2 is disabled by default, but it doesn't harm to explicitly disable it again. SSLv3 is vulnerable to an attack called POODLE, so we will disable it too. In the same file, find the ssl_protocols parameter line, uncomment it and add !SSLv3 to the end, like this:

ssl_protocols = !SSLv2 !SSLv3

Edit 02/09/2017: if you're using Debian Stretch or later, or one of its derivatives, then you will need to edit that line to match the following. The SSLv2 option is no longer recognised as an option for ssl_protocols because it has been removed entirely:

ssl_protocols = !SSLv3

For some bizarre reason, the Dovecot package for Raspberry Pi (and possibly newer versions of Ubuntu) does not create a self-signed certificate during installation like it used to. So, we have to create one manually. If you look in /usr/share/dovecot/ you will find the script that used to be used to generate the certificate; we can use it ourselves to simplify the process.

The script is located at /usr/share/dovecot/mkcert.sh and looks like this:

#!/bin/sh

# Generates a self-signed certificate.
# Edit dovecot-openssl.cnf before running this.

OPENSSL=${OPENSSL-openssl}
SSLDIR=${SSLDIR-/etc/ssl}
OPENSSLCONFIG=${OPENSSLCONFIG-dovecot-openssl.cnf}

CERTDIR=/etc/dovecot
KEYDIR=/etc/dovecot/private

CERTFILE=$CERTDIR/dovecot.pem
KEYFILE=$KEYDIR/dovecot.pem

if [ ! -d $CERTDIR ]; then
  echo "$SSLDIR/certs directory doesn't exist"
  exit 1
fi

if [ ! -d $KEYDIR ]; then
  echo "$SSLDIR/private directory doesn't exist"
  exit 1
fi

if [ -f $CERTFILE ]; then
  echo "$CERTFILE already exists, won't overwrite"
  exit 1
fi

if [ -f $KEYFILE ]; then
  echo "$KEYFILE already exists, won't overwrite"
  exit 1
fi

$OPENSSL req -new -x509 -nodes -config $OPENSSLCONFIG -out $CERTFILE -keyout $KEYFILE -days 365 || exit 2
chmod 0600 $KEYFILE
echo 
$OPENSSL x509 -subject -fingerprint -noout -in $CERTFILE || exit 2

If you were going to use this certificate for any significant length of time, it would be worth editing the parameters in the config file it uses (/usr/share/dovecot/dovecot-openssl.cnf) to set the proper common name and contact details on the certificate. However, I suggest you leave the defaults as they are, use this certificate just for testing, and then come back later and generate a new cert when everything is working (more on that later).

You must be in the same folder as the configuration file when you run the script, or it will not find the config and the certificate generation will fail. The following two commands will change to the right folder and then execute the script:

cd /usr/share/dovecot
sudo ./mkcert.sh

You should see a message "writing new private key to '/etc/dovecot/private/dovecot.pem'" and then some details about the certificate.

Next, find the following two lines in /etc/dovecot/conf.d/10-ssl.conf and uncomment them:

#ssl_cert = </etc/dovecot/dovecot.pem
#ssl_key = </etc/dovecot/private/dovecot.pem

Now reload dovecot to apply the changes:

sudo service dovecot reload

Since IMAPS is a connection over SSL/TLS, we can’t use Telnet to test it. Instead, we use openssl to create a secure connection. There are two versions of the command, one will show you LOADS of information about the certificate used to encrypt the connection, and the other will suppress this info. I recommend trying the long version out of interest, but both will work the same for the test:

For full information:

openssl s_client -connect localhost:993

For minimal information:

openssl s_client -connect localhost:993 -quiet

I won’t print the output of the first command, because it’s ridiculously long. Here’s an example of the second, including a login test:

admin@samhobbs /etc/dovecot/conf.d $ openssl s_client -connect localhost:993 -quiet
depth=0 O = Dovecot mail server, OU = samhobbs, CN = samhobbs, emailAddress = root@samhobbs.co.uk
verify error:num=18:self signed certificate
verify return:1
depth=0 O = Dovecot mail server, OU = samhobbs, CN = samhobbs, emailAddress = root@samhobbs.co.uk
verify return:1
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
a login "testmail" "test1234"
a OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE] Logged in
b logout
* BYE Logging out
b OK Logout completed.
Connection closed by foreign host.

Good stuff: SSL/TLS is working on port 993, and you can log in successfully.

Note that by default Dovecot uses a “snakeoil” self-signed certificate. SSL/TLS certificates are used for two purposes: encryption and verification. The “snakeoil” certificate will encrypt your content but it won’t verify that you’re talking to your server – you could be talking to someone imitating your server (anyone can create a self-signed certificate claiming to be any website).

If you’d like to get your certificate signed without forking out loads of money to a cert signing authority, I’d recommend CAcert. I've written a tutorial explaining how to generate your own cert and get it signed here. If you opt for a commercial certificate, you can use the CAcert tutorial to generate the certificate and then this tutorial will explain the differences in the installation/configuration of commercial certificates once you have it signed.

If you're testing a proper certificate, use this command to tell openssl where the trusted root certificates are stored:

openssl s_client -connect localhost:993 -quiet -CApath /etc/ssl/certs

Tidying up and enabling WAN access

Before opening the ports on your router to the world, it’s a good idea to delete that test user because the password is so easy to guess.

sudo userdel testmail

Also, if you still use the "pi" login, for goodness' sake change the password from "raspberry"! You can do this using the passwd command when logged in as pi:

passwd

Or you can achieve the same thing when logged in as another user by using sudo to gain root privileges:

sudo passwd pi

Now you can open a few ports on your router’s firewall. Make sure your Pi has a static LAN IP address and then forward these ports from WAN to its LAN IP address:

  • Port 25 for SMTP (used for receiving emails)
  • Port 465 for secure SMTP (used for sending emails after SASL authentication)
  • Port 993 for IMAPS (used to receive emails on your phone/tablet/computer)

Here’s an example on my router, running OpenWrt:

openwrt-port-forwards-raspberry-pi-email-server.png

Setting up IMAP Email Clients

I’m now going to run through setting up IMAP email clients quickly, using K9 Mail on Android and Thunderbird on GNU/Linux as examples. The setup for Thunderbird on Windows and Mac OSX should be very similar.

The basics are this:

  • Select an IMAP connection
  • Your login is your username only (omit @yourdomain.com), and you password is…your password!
  • For incoming emails: select use SSL/TLS always and the program should automatically select port 993
  • For outgoing emails: select SSL/TLS always. The program may suggest port 587, but you want port 465

K9 Mail

Open K9 Mail and select add new account. Type in your account information (you@yourdomain.com and password) and then select manual setup. Select IMAP and then enter your information as follows…

Incoming email:

K9 Incoming Email Settings

Outgoing email:

K9 Outgoing Email Settings

Thunderbird

Open Thunderbird, and then click Account Actions –> Add Mail Account.

Fill in your password and email address, which is your username followed by your fully qualified domain name (FQDN), i.e. username@yourdomain.com:

Thunderbird Step 1: Mail Account Setup

Thunderbird will try to auto-detect settings and fail. Don’t worry, this is normal. Select “manual config”:

 Thunderbird Step 2: TB will try to autodetect settings, and fail. Select “Manual Config"

Now edit the settings as appropriate. I had to remove a period (.) from in front of my “server hostname”, and edit the SSL and Authentication settings. If you select “SSL/TLS” for both incoming and outgoing, ports 993 and 465 are automatically selected:

Thunderbird Step 3: Edit the settings so that they match these (but change them to match your username and domain name!)

Now try emailing yourself from your external email address, and see if your email gets through. If you are having problems, be sure to check you’ve set up an MX record as well as a DNS A record.

Stuck in spam filters?

A few people have contacted me recently to say that their email server is working fine but their emails are getting sent to Gmail's spam folder.

If you are experiencing problems like this (or even if you're not), try setting up an SPF and/or PTR record as explained in my DNS basics tutorial.

You might also want to check if your domain name or IP address are on any blacklists. There's a handy website called MX toolbox that lets you do this (choose blacklist check from the dropdown menu).

Almost done…

Good news! If you’ve reached this far and everything is working, then you’re almost done. The next step (Webmail with Squirrelmail) is optional but by far the easiest of the three steps.

If you’ve hit a rut, please post a comment and I’ll try and help you out.

If not… continue to Raspberry Pi Email Server Part 3: Squirrelmail

Type: 

Comments

George,

You'll have to give me a bit more time to respond to your comments, I'm at work at the moment (currently on my lunch break).

You say that the instructions are not clear and I accept that I could probably improve the wording. However, if you read what I have written carefully you will find that the tutorials contain all the information you need. Many of your other questions have also been answered in the tutorials...

For example, the Squirrelmail tutorial you are following says this:

The configuration script creates a configuration file for apache in /etc/squirrelmail/apache.conf. You need to create a symbolic link so that Apache2 will load your Squirrelmail apache configuration file when it starts up:
sudo ln -s /etc/squirrelmail/apache.conf /etc/apache2/conf.d/squirrelmail.conf

So, the file for Squirrelmail's apache configuration is at /etc/squirrelmail/apache.conf, and you have symlinked it to /etc/apache2/conf.d/squirrelmail.conf. You can open the file using either of these paths, e.g.:

sudo nano /etc/apache2/conf.d/squirrelmail.conf

or

sudo nano /etc/squirrelmail/apache.conf

...and make your changes there.

If you use the default file with the Alias statements in it, it will affect each of your virtualhosts, e.g. domain1.com/squirrelmail and domain2.com/squirrelmail would both load the squirrelmail config page. If you change it to contain a whole virtualhost block then it is completely separate and will not affect your other virtualhosts.

One possible reason for the error is that the virtualhost in the default-ssl file and the virtualhost block in your Squirrelmail apache config file contain the same servername so you have a conflict between your two virtualhosts, but it's difficult to tell because you haven't told me what is on line 43 of /etc/apache2/sites-enabled/default-ssl!

One more thing... when you say this:

I was able to bring up Squirrel on my main computer and I can run it as a local host.

I think you mean that you are viewing squirrelmail from your main computer in a web browser, and you can also view squirrelmail with the Pi's web browser, but I'd just like to check you don't mean you have installed squirrelmail on your main computer?

Sam

Hi Sam, sorry I haven't replied earlier, our ISP managed to sever a line and internet has been out for most of the city for the last two days.
In answer to your question, yes Squirrel is hosted on the Raspberry Pi and I can open a web-browser on a Windows PC and type in mydomainname/squirrelmail and it opens the squirrel mail website. So all that is as it should be according to your instructions. The next bit is to then follow the instructions after "if you would like to serve webmail on https only..." You show blocks of code but it is not clear to me which file I am supposed to be modifying.

Modify your squirrelmail Apache config file, using either of the paths I gave in the comment you just replied to.

When entering my email and password into Thunderbird, it finds a configuration "using common server names". However, this configuration uses STARTTLS for incoming and outgoing mail, as well as using port 143 for incoming and port 25 for outgoing. When I change the ports to 993 and 465, respectively, I cannot connect. However, the configuration given to me by Thunderbird can connect.

Although this works, I would not recommend you use it. You will not always be able to send email using port 25 because some ISPs block that port (say for example you take your laptop to someone else's house and try to send an email from there - port 465 would still work if 25 was blocked).

Are you sure you've forwarded the right ports on your router? What's your domain name?

Sam

I just tried connecting to your server with openssl and your ports are fine:

feathers-mcgraw@Hobbs-T440s:~$ openssl s_client -connect sw3dish.me:465 -quiet
depth=0 CN = *.sw3dish.me
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 CN = *.sw3dish.me
verify error:num=27:certificate not trusted
verify return:1
depth=0 CN = *.sw3dish.me
verify error:num=21:unable to verify the first certificate
verify return:1
220 sw3dish.me ESMTP Postfix (Debian/GNU)
ehlo samhobbs.co.uk
250-sw3dish.me
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-AUTH PLAIN LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
quit
221 2.0.0 Bye
feathers-mcgraw@Hobbs-T440s:~$ openssl s_client -connect sw3dish.me:993 -quiet
depth=0 CN = *.sw3dish.me
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 CN = *.sw3dish.me
verify error:num=27:certificate not trusted
verify return:1
depth=0 CN = *.sw3dish.me
verify error:num=21:unable to verify the first certificate
verify return:1
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
a logout

When you select 993 and 465 do you have SSL/TLS selected? It has to be SSL/TLS, not STARTTLS on these ports.

Sam

Huh, it seems to be working now. When I went to manual configure the settings for a new account in Thunderbird and clicked "re-test", Thunderbird wouldn't accept the SSL/TLS settings. However, I was able to get it to accept the settings without testing and it works fine.

Regarding the SSL verify errors: I used your CACert tutorial to create a certificate -- is this normal and just related to the CACert process?

Strange, have you reloaded/restarted postfix or dovecot since you were messing around initially?

Anyway, I just learned something cool thanks to your question. If you look in your certs directory ls -l /etc/ssl/certs you will see that all of the certs have sensible certificate names like GeoTrust_Global_CA.pem, but there are also a load of symbolic links with names like 2c543cd1.0 that point to the human readable cert names.

Apparently, the symlink names like 2c543cd1.0 are hashes of the certificate files, and enable programs on your computer to quickly check whether the root certificate is in your computer's certificate directory or not. Some programs manage fine without the symlinks, but some do not. It looks like openssl is one of the ones that doesn't.

So, in my CAcert tutorial I actually missed a step, which is the command used to refresh all of those symlinks (we installed the CACert root certificate but it doesn't yet have a symlink):

sudo c_rehash /etc/ssl/certs

And now...

feathers-mcgraw@Hobbs-T440s:~$ openssl s_client -connect mail.sw3dish.me:993 -quiet -CApath /etc/ssl/certs
depth=1 O = Root CA, OU = http://www.cacert.org, CN = CA Cert Signing Authority, emailAddress = support@cacert.org
verify return:1
depth=0 CN = *.sw3dish.me
verify return:1
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
a logout

Ta da! :D

You might also have noticed that when I connected the first time I tried just sw3dish.me, so the certificate wouldn't have matched because of the wildcard and I would have got a different error.

Anyway, thanks again for asking an interesting question! I'll have to update my CACert tutorial.

Sam

If you are not going to cover how to install postfixadmin can you at least teach how to add new email accounts to postfix and dovecot?

No need to get your knickers in a twist. Part 2 of the tutorial actually explains how to add a new user (testuser), did you miss that step?

The setup here is for each user to be a "real" system user with a home directory like /home/sam/, so to add a new user all you do is:

sudo adduser sam

Your postfix and dovecot username & password are the same, because they're your system username and password.

Since adding a new system user requires superuser privileges, you wouldn't want to hand this over to something like postfixadmin (and therefore Apache) - that would be asking for trouble. I guess postfixadmin only works when postfix is set up for virtual users, in which case adding a username would not affect the whole system and would not require superuser privileges.

Hi Sam
when I restart dovecot i have the following lines. It is correct?

sudo service dovecot restart
doveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf line 89: Unknown setting: unix_listener
[....] Restarting IMAP/POP3 mail server: dovecotdoveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf line 89: Unknown setting: unix_listener
failed!

Hello again! Not sure exactly what you mean by "is it correct" - Dovecot is correct that you have an error in your configuration file.

If I had to guess, I'd say you have something like this in the file:

#service auth {
        unix_listener /var/spool/postfix/private/auth {
                mode = 0660
                user = postfix
                group = postfix
        }
}

(commented the start of service auth { by accident) or even just

unix_listener /var/spool/postfix/private/auth {
                mode = 0660
                user = postfix
                group = postfix
        }

i.e. the unix_listener parameter is not inside the service auth {...} block of code - this would explain the Dovecot error: the parameter makes sense inside the block but not as a standalone configuration option, hence it's an "unknown setting".

If that's not it, please post the relevant section of your config file showing the start and end of the service auth {...} block.

Sam

Hi Sam, this is the part of unix_listener in my file

#service auth {
unix_listener /var/spool/postfix/private/auth {
mode = 0660
user = postfix
group = postfix
}
}

What a guess :) spot on!

Uncomment the service auth { line and restart postfix.

Sam

This is my part of service auth but it doesn't work

service auth {
unix_listener /var/spool/postfix/private/auth {
mode = 0660
user = postfix
group = postfix
}
}

This is the error when I try to restart Dovecot

[....] Restarting IMAP/POP3 mail server: dovecotdoveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf line 66: Unknown setting: service
failed!

Thank you

I notice the line number in the error has changed, do you have another service auth block earlier in the file?

Sam

This is my file:

#default_process_limit = 100
#default_client_limit = 1000

# Default VSZ (virtual memory size) limit for service processes. This is mainly
# intended to catch and kill processes that leak memory before they eat up
# everything.
#default_vsz_limit = 256M

# Login user is internally used by login processes. This is the most untrusted
# user in Dovecot system. It shouldn't have access to anything at all.
#default_login_user = dovenull

# Internal user is used by unprivileged processes. It should be separate from
# login user, so that login processes can't disturb other processes.
#default_internal_user = dovecot

service imap-login {
inet_listener imap {
#port = 143
}
inet_listener imaps {
#port = 993
#ssl = yes
}

# Number of connections to handle before starting a new process. Typically
# the only useful values are 0 (unlimited) or 1. 1 is more secure, but 0
# is faster.
#service_count = 1

# Number of processes to always keep waiting for more connections.
#process_min_avail = 0

# If you set service_count=0, you probably need to grow this.
#vsz_limit = $default_vsz_limit
}

service pop3-login {
inet_listener pop3 {
#port = 110
}
inet_listener pop3s {
#port = 995
#ssl = yes
}
}

service lmtp {
unix_listener lmtp {
#mode = 0666
}

# Create inet listener only if you can't use the above UNIX socket
#inet_listener lmtp {
# Avoid making LMTP visible for the entire internet #address =
#port =
#}

service imap {
# Most of the memory goes to mmap()ing files. You may need to increase this
# limit if you have huge mailboxes.
#vsz_limit = $default_vsz_limit

# Max. number of IMAP processes (connections)
#process_limit = 1024
}

service pop3 {
# Max. number of POP3 processes (connections)
#process_limit = 1024
}

# Postfix smtp-auth
#unix_listener /var/spool/postfix/private/auth {
# mode = 0666
#}

# Auth process is run as this user.
#user = $default_internal_user
}

service auth-worker {
# Auth worker process is run as root by default, so that it can access
# /etc/shadow. If this isn't necessary, the user should be changed to
# $default_internal_user.
#user = root
}

service dict {
# If dict proxy is used, mail processes should have access to its socket.
# For example: mode=0660, group=vmail and global mail_access_groups=vmail
unix_listener dict {
#mode = 0600
#user =
#group =
}
}
service auth {
unix_listener /var/spool/postfix/private/auth {
mode = 0660
user = postfix
group = postfix
}
}

I have service auth-worker in the file...

I think I've spotted the error: your service lmtp block doesn't have a closing bracket. It should look like this:

service lmtp {
  unix_listener lmtp {
    #mode = 0666
    mode = 0666
  }

  # Create inet listener only if you can't use the above UNIX socket
  #inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    #address =
    #port = 
  #}
}

Mine actually looks like this:

service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    #mode = 0666
    mode = 0666
  }

  # Create inet listener only if you can't use the above UNIX socket
  #inet_listener lmtp {
    # Avoid making LMTP visible for the entire internet
    #address =
    #port = 
  #}
}

(full path to lmtp) but try the top one first.

Sam

Hi Sam
the service does not start again...

What was the error message, and which configuration did you use?

Sam

Hi Sam.
The error is this

doveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf line 1: Expecting '='
[....] Restarting IMAP/POP3 mail server: dovecotdoveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf line 1: Expecting '='
failed!

Hello again Sam,
thank you for your reply. At the moment the raspberry is down beacause I installed Owncloud with your guide. I need to upgrade owncloud to the lastest version i try to download and unzip the file but it doesn't work. For the email server, I will do the things in your reply.
Sorry for my english (I'm not english...)
Thanks again Sam :)

Sam

Many thanks for your tutorials. They are much clearer than anything else I have come across; and more importantly, everything works.

I've set up an email server and it's working well. I am wondering whether there is a ready way of setting up a backup to automatically receive mail etc if the primary server ever fails and I'm not around to fix it?

Stephen

Thank you, and you're welcome!

Your MX record can list more than one hostname for servers to try when delivering email to you. You could set up another pi (at your parents' house, perhaps?) so that you continue accepting email even when your internet connection is down, and then use fetchmail or something similar to pull the email from it to the main Pi.

I've been thinking about doing something like this for a while, but I don't think it will be a trivial solution - spammers sometimes select the lowest priority server to deliver their mail to in the hope that it will have worse spam filtering than the main server. You've also got to consider what happens when the main pi is down and you want to send mail out - do you set up the secondary pi to route email through your parents' ISP's SMTP server? When the main pi is down and your email client connects with IMAP, how does it deal with all of the email it thought was in the inbox suddenly being missing? I'm not sure if it would be necessary to sync the two Maildirs on the servers or something. I'm sure someone must have come up with a sensible solution to these problems but I haven't had time to research it properly yet.

Sam

Hello. First I want to thank you for your guides.

I have a problem with my certificate. Every time I open Outlook I get an error message saying:
"The server you are connecting to is using a security certificate that cannot be verified"

I guess it's the problem with my security certificate not matching my domain name (mail.domain.com).

How do I change it on my RPI?

More info:

depth=0 CN = raspberrypi
verify error:num=18:self signed certificate
verify return:1
depth=0 CN = raspberrypi
verify return:1

No, I didn't see that tutorial. I have followed that and everything is working now!! Great

Thank you

Hi Sam. Used this brilliant tutorial to set my pi up as a mail server and it's been working beautifully for a while now. However, I'm currently on the move and just tried to access my email remotely. No dice. I can't retrieve any mail. I tested with the command "openssl s_client -connect "mydomain":993 -quiet" but it returns a connection timed out message with error number 145. If I check my email at home all is fine. Any advice appreciated.

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