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

Hi, My emails dont seem to be getting out to anyone as most spam filters pick it up as spam. I''ve looked into this, and think its due a SMTP Reverse DNS Mismatch? any ideas on how to resolve this?

Also, not getting any emails in, as apparently i have no inbox?? all credentials validate in thunderbird validate...

A reverse DNS check is where the other server looks up the PTR record (see my most recent tutorial, also linked in this article) for your IP address and checks that the result matches the hostname you used to EHLO.

Normally services like Gmail need a PTR or an SPF record before they accept your email.

As for the mailbox, check the maildir exists for your user and that you haven't missed the "tell dovecot where your mailbox is" step in this tutorial... people always miss that, I don't know why!

Sam

Hi Sam,

Firstly - these tutorials are first rate - some of the best I cam come across and something you should be incredibly proud of!
However...if I could have a little help I would be very appreciative!

I have my mail working and redirected (just my mail for now) to https but despite having a wildcard CACert nothing I do gets the certificate to be recognised as authorised!

When I do this:

openssl s_client -connect localhost:993 -quiet

I get the following results (truncated to get through spam filters):

depth=0 CN = *.arkadiem.co.uk
verify error:num=20:unable to get local issuer certificate
verify error:num=27:certificate not trusted
verify error:num=21:unable to verify the first certificate

I am only getting a CN, unlike your example where you have the OU and CN.
I have not put the mail.arkadiem.co.uk into action yet (web server is on another pi!) but instead using the https://arkadiem.co.uk/squirrelmail so you can see for yourself.

Where do you think i'm going wrong??

Cheers
Dan

Hi,

Thank you, I'm glad you're finding it useful!

If you want to do certificate verification with openssl you have to pass the path as an option (I should add this to the tutorial - the default with openssl is to only check what you specifically tell it to, whereas the default for most programs like web browsers is to trust any root cert in your certificate path). I'll check this when I get home, but I think the command is:

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

Also, I'm guessing you know this and you have a mismatch temporarily, but I'll say it anyway for the record... a wildcard cert is good for anything.yourdomain.com , but can't be used for yourdomain.com - you must have a subdomain! So you can either re-generate a cert for yourdomain.com or serve squirrelmail on www.yourdomain.com (similarly for your mail server - if the host name is mail.yourdomain.com then a wildcard is fine but if not you'll want a plain yourdomain.com cert. The great thing about CACert is that it's free so you can mix and match if you like (get a wildcard cert and a normal cert signed, and use one for mail (yourdomain.com) and the other for www.yourdomain.com).

My setup now is to have everything on samhobbs.co.uk (no subdomain) because I'm using a commercial cert and wildcards are more expensive (even more expensive than two certs for specific subdomains!).

Decide how you want everything set up and I'll help you if you have any problems.

Sam

Thanks Sam,

Yes the mis-match was intentional initially as I intend to merge the web server and mail server pi's as I took receipt last week of a Raspberry Pi 2 (which is what the new mail server is built on!)

Anyhoo...I had initially started with a SSL for just arkadiem.co.uk with the same results!

The results of the above code is:

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 = arkadiem.co.uk
verify return:1
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.

This does indeed suggest a miss-match in the CACert generation.
Did I just miss those fields when creating the SSL for OU and e-mail address??

Many thanks
Dan

My Pi 2 arrived in the post today, I forgot to order a case and micro SD card for it though so it'll have to wait a bit longer!

The OU and email address fields are some of the ones that get stripped by CAcert - since it's an automated service, they don't verify that those parts are correct, so they take them out - they're just signing to say that you control the domain name.

Sam

The Pi2 is a monster and a game changer!! If you have a B+ the same case fits!!

Are the restrictions with the CACert the reason you went with a purchased one?
Is it not possible with CACert to get the green padlock then? As I would only use it for squirrelmail its not massively essential but I would like to encrypt my site when I put it all together in a similar fashion as you have done!

Cheers
Dan

Unfortunately all of my current pi are model B... the one behind my TV is the 256 MB RAM version, I'm always impressed with how much it's capable of! The Pi 2 must be really quick in comparison!

See here for details of how and why I installed a commercial cert.

You can get the green padlock with cacert but only if you have the root certificate installed, so it's good for services you use yourself but not the general public.

Sam

Cheers Sam,

That suddenly all makes sense with the SSL, thanks again!
Good luck with the Pi2 fun - I certainly am :)

Dan

First off, thanks for the great tutorial! Very well documented and detailed. So, I made it all the way to setting up imap clients. I have successfully set up both mobile and thunderbird accounts using the parameters you gave in the tutorial. I can send mail fine, and i can receive mail from other users on the pi; but I cannot receive mail from my gmail account. When I do send a message from my external (gmail) account, the message is not bounced back and seems to be delivered correctly. However, it never makes it to my inbox. I have gone over and over the config files and MX settings, and everything appears to be correct. Could you please email bob@forchaengineering.com and let me know what your mail.log shows after? Also, could you check my MX settings (forchaengineering.com) and let me know if anything looks off?
Thanks again for all the help,
Bob

So what about POP3? I noticed with the configuration like this POP3 wont work. I agree its insecure and Dovecot really was not meant for it, but it is a legacy protocol and offers a good fallback. What is missing in the configs to get POP3 going?

Hi Chris,

My reason for not configuring POP wasn't that it's insecure, I just don't think it's at all useful. The only time I can see that you would want to use it is if you're fetching email from someone else's server and you don't want them to keep a copy once you have retrieved it.

It should be fairly trivial to get pop working, but what's your use case?

See this comment if you really want to use POP.

Sam

The main use case is to make the transition of existing POP accounts to IMAP(S) accounts easier on the 'less technical' user base as well as maintaining copies of mail on the mail server itself for those 'shared' mailboxes. Additionally, IMAP does put more of a traffic load on a PI because the transactions between client and server are constantly synced, and can cause "stuttering" on mobile connections. Reading through the comment you linked to, it just seems I was missing the POP daemon, all seems good now once the daemon was fully installed for dovecot.

Thanks for great articles and assistance..much appreciated...

Regards,
Chris

That's fair enough :)

Out of interest, how many people are using your Pi email server? I didn't think anyone would be using it for something more than just a family server, but it sounds like you are, which is pretty cool!

Sam

Funny enough it is a family mail server, the issue is everyone in the family has their own domains and various levels of skills. Fortunately the traffic is low (and I have a PI 2 arriving next week to migrate to), but I do like to 'monitor' my children mailboxes, and POP is great for that as well. I am using another PI running ASSP for SPAM filtering so I only went so far as POSTFIX and DOVECOT for the mail server, and then ASSP for SPAM proxy on another PI, so overall daemon load on the mail server is just the two services, so that also helps with overhead.

Honestly, these PI's are too damn cheap and I find myself just buying a bunch and separating out what used to be multiple services on one box to now specializing on individual PI's and just moving traffic around on the local network. Upside is I am using much less power (and so much quieter) then before..downside of course is I have a set of PI's to take care of and SD cards that wont last as long as a SSD or magnetic media (PI's using NAS for storage is the next project once I get a new enclosure to replace an old Storango I have).

Regards,
Chris

I think it's pretty cool that you provide email for your family like that. It's a bit unsettling that the default is to sign up with one of the megacorps who are, of course, trying to monetise the service in some way...many of those services have serious privacy issues.

I am continually surprised that anyone can afford to make a Pi B at the current price and turn a profit. They are amazing little machines, and the movement has built up some real momentum! Like you said, they're so cheap that you might as well have them doing specialised jobs - one of mine is a print server, for example. Two are Raspbmc / XBMC boxes. My boss has one set up as a camera pointed at his fish tank. Why not? :)

Best of luck with your projects, and thanks for the comment :)

Sam

I have everything just about working but I am have difficulty with Thunderbird.

With one of the account Thunderbird accepts the server certificate and verifies it correctly. This account is an admin on Win 7 and received the original mail probe (as root) when I set the certificate up. I can setup the other accounts in this profile (with the verified server certificate) with no issues.

When I try to connect with other account Thunderbird refuses to verify the server certificate, despite the root certificates being in place and verified.

Sam

I followed your tutorial without an issue

Could it to be the way I am creating the certificate locally on my windows machine. I copy the cert as text and paste it into a text document saving it with an extension. I have tried .crt and .pem with no success. Is notepad ++ or Windows notepad amending the text with hidden characters?

I tried (got blocked) to post a section of the mail log which seems to show that Thunderbird doesn't sen the user name to Dovecot. Is that because it doesn't like the certificate? It does sen the user name with the profile that works.

Was commenting out the Snakeoil certificates when I installed the CA certificate a bad idea

Is it a CAcert certificate, or a commercial cert?

If it's a CAcert certificate, the most likely reason for the failure is that you don't have the CAcert root installed in Thunderbird.

If you can tell me your domain name I'll do some tests with you to figure out what is happening.

Sam

Sorry Sam

The certificate is a CAcert certificate

My domain is timandlani.com

Tim

Tim,

You appear to be using a wildcard cert (*.timandlani.com), so unless your users are connecting to you via a subdomain like mail.timandlani.com the common name on the cert won't match. Wildcard certs match any subdomain (mail.yourdomain.com, www.yourdomain.com), but not the root domain!

Sam

Sam

Sorry for stating the blindingly obvious, but I will

I need to generate a non-wildcard certificate (timandlani.com) OR put the mail server on a sub domain to get the wildcard certificate to work.

Which lead me to another question. In one of your fabulous tutorials is there a section on how I would combine two server certificates if I went down the second certificate route?

You got it. You can generate more than one cacert certificate by the way (one normal one wildcard), and then just use the wildcard one for www./Apache and the normal one for your email server if that's what you'd like to do?

Sam

Hi Sam, Firstly i must congratulate you on a very well written tutorial, It worked for me pretty much as you said it would.
I was wondering if you have had any experience in setting up POP3 as opposed to IMAP, (i just preffer it).
And secondly when i login to squirel mail on my LAN i have no problems, but if i going through my domain i get authentication errors! Any thoughts?

Hello Sam,

once you have configured the ssl/tls method for retrieving with imaps on port 993 why do you keep imap open on port 143.
A client misconfigured could send many times his password in clear while performing imap.

Thank you for your excellent tutorial that I tested on a respberry pi and that I am implementing on a VPS because e-mail from an adress listed as dynamic is not a good idea.
Maybe we need to configure /etc/dovecot/conf.d/10-master.conf as follow.

Best regards.
Christian

################### /etc/dovecot/conf.d/10-master.conf ####################
service imap-login {
# inet_listener imap {
# port = 143
# }
inet_listener imaps {
port = 993
ssl = yes
}

Christian,

It's good you're thinking about this. It actually doesn't matter if you're hosting at home on ar raspi behind a router, since the router's firewall blocks 143 unless you port forward it (and I've said not to). You're right that it does matter on a VPS since you don't have the router firewall, and the changes you have suggested are sensible.

The reason I didn't stop listening on 143 is so that squirrelmail doesn't have the overhead of the TLS connection just to connect to localhost, but I don't think it really affects the speed that much even for a pi.

Thanks for an interesting comment!

Sam

Hi Sam,

If this is set up properly, would email still be stored by my hosting service? I can still access webmail through their interface (hostmonster) and see mail that I've sent and received there.

Is there anything special to do when setting up a MX record?

I'm confused how the instructions here would alter settings on my hosting service?

Thanks,

Glenn

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