• Install Raspberry Pi OS on Pi Board
• Ensure SSH access to Pi

sudo apt-get update
sudo apt-get install postfix
sudo apt-get install dovecot-common dovecot-imapd

Select 'Internet Site' and then set the mail name to your domain name. In this article, I refer to the domain name as example.com

cd /etc/postfix/
sudo nano /etc/postfix/main.cf

Edit the following:

myhostname = example.com

Add the following:

inet_protocols = ipv4
home_mailbox = Maildir/
mailbox_command =
smtpd_recipient_restrictions =
   permit_sasl_authenticated,
       permit_mynetworks,
       reject_unauth_destination
smtpd_helo_required = yes
smtpd_helo_restrictions =
       permit_mynetworks,
       permit_sasl_authenticated,
       reject_invalid_helo_hostname,
       reject_non_fqdn_helo_hostname,
       reject_unknown_helo_hostname,
       check_helo_access hash:/etc/postfix/helo_access
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_tls_auth_only = yes
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301

Ctrl-X to exit, and Y to save.

sudo maildirmake.dovecot /etc/skel/Maildir
sudo maildirmake.dovecot /etc/skel/Maildir/.Drafts
sudo maildirmake.dovecot /etc/skel/Maildir/.Sent
sudo maildirmake.dovecot /etc/skel/Maildir/.Spam
sudo maildirmake.dovecot /etc/skel/Maildir/.Trash
sudo maildirmake.dovecot /etc/skel/Maildir/.Templates
sudo maildirmake.dovecot /etc/skel/Maildir/.Junk
sudo cp -r /etc/skel/Maildir /home/pi/
sudo chown -R pi:pi /home/pi/Maildir
sudo chmod -R 700 /home/pi/Maildir
sudo nano /etc/postfix/helo_access

Add the following:

example.com   REJECT          Email rejected - cannot verify identity
mail.example.com      REJECT          Email rejected - cannot verify identity

Ctrl-X to exit, and Y to save.

sudo postmap /etc/postfix/helo_access
sudo nano /etc/dovecot/dovecot.conf

Edit:

listen = *

Ctrl-X to exit, and Y to save.

sudo nano /etc/dovecot/conf.d/10-mail.conf

Edit:

mail_location = maildir:~/Maildir

Ctrl-X to exit, and Y to save.

sudo nano /etc/dovecot/conf.d/10-master.conf

Edit:

service imap-login {
 inet_listener imap {
   port = 143
 }
 inet_listener imaps {
   port = 993
   ssl = yes
 }
}
service auth {
   unix_listener /var/spool/postfix/private/auth {
               mode = 0660
               user = postfix
               group = postfix
       }
}

Ctrl-X to exit, and Y to save.

sudo nano /etc/dovecot/conf.d/10-auth.conf

Edit:

disable_plaintext_auth = no
auth_mechanisms = plain login

Ctrl-X to exit, and Y to save.

sudo nano /etc/dovecot/conf.d/10-ssl.conf

Edit:

ssl = yes
ssl_protocols = !SSLv3
ssl_cert = </etc/letsencrypt/live/example.com/fullchain.pem
ssl_key = </etc/letsencrypt/live/example.com/privkey.pem

You will note that rather than building a new SSL certificate, we are leveraging the certificate from Let's Encrypt that was already previously built.

Ctrl-X to exit, and Y to save. Now you will need to use the below “adduser” command to add each email address that you wish to set up. For example, to set up joedoe@example.com:

sudo adduser joedoe

Open this file:

sudo nano /etc/postfix/master.cf

Add:

-o content_filter=spamassassin

Bellow this line:

smtp   inet  n       -       y       -       -       smtpd

Add:

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

Bellow this line:

smtps     inet  n   -       -       -       -       smtpd

So it will look something like this:

...
smtp   inet  n       -       y       -       -       smtpd
        -o content_filter=spamassassin
#smtp      inet  n       -       y       -       1       postscreen
#smtpd     pass  -       -       y       -       -       smtpd
...
smtps     inet  n       -       -       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject

Add this to the end of the file:

spamassassin    unix  -   n       n       -       -       pipe user=debian-spamd argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}

Ctrl-X to exit, and Y to save.

sudo apt-get install opendkim opendkim-tools
sudo nano /etc/opendkim.conf

Add or edit (if exist) as below:

AutoRestart   Yes
AutoRestartRate         10/1h
SyslogSuccess           Yes
LogWhy                  Yes
Canonicalization        relaxed/simple
ExternalIgnoreList      refile:/etc/opendkim/TrustedHosts
InternalHosts           refile:/etc/opendkim/TrustedHosts
KeyTable                refile:/etc/opendkim/KeyTable
SigningTable            refile:/etc/opendkim/SigningTable
Mode                    sv
PidFile                 /var/run/opendkim/opendkim.pid
SignatureAlgorithm      rsa-sha256
UserID                  opendkim:opendkim
Socket                  inet:12301@localhost

Ctrl-X to exit, and Y to save.

sudo nano /etc/default/opendkim

Edit:

SOCKET="inet:12301@localhost"

Ctrl-X to exit, and Y to save.

sudo mkdir /etc/opendkim
sudo mkdir /etc/opendkim/keys
sudo nano /etc/opendkim/TrustedHosts

Add:

127.0.0.1
localhost
192.168.0.1/24
*.example.com

Also add your pi's local ip address in there. You can find it by this command: hostname -I

Ctrl-X to exit, and Y to save.

sudo nano /etc/opendkim/KeyTable

Add:

mail._domainkey.example.com example.com:mail:/etc/opendkim/keys/example.com/mail.private

Ctrl-X to exit, and Y to save.

sudo nano /etc/opendkim/SigningTable

Add:

*@example.com mail._domainkey.example.com

Ctrl-X to exit, and Y to save.

cd /etc/opendkim/keys
sudo mkdir example.com
cd example.com
sudo opendkim-genkey -s mail -d example.com
sudo chown opendkim:opendkim mail.private
sudo chmod 777 mail.txt
sudo nano -$ mail.txt

Go to your domain registrar (e.g., CloudFlare, EuroDNS, GoDaddy, etc.). Use this output to set up a TXT record, with hostname: mail._domainkey and with value: v=DKIM1; k=rsa; p=MIG….

sudo service dovecot reload
sudo service dovecot restart
sudo service postfix reload
sudo service postfix restart
sudo service opendkim restart

sudo apt-get install spamassassin
sudo nano /etc/spamassassin/local.cf

Edit:

rewrite_header Subject [***** SPAM _SCORE_ *****]
report_safe 0
required_score 5.0
use_bayes 1

Ctrl-X to exit, and Y to save.

sudo nano /etc/default/spamassassin

Edit:

ENABLED=1

Ctrl-X to exit, and Y to save.

sudo service spamassassin start
sudo systemctl enable spamassassin
sudo service dovecot restart
sudo service postfix restart

If you use Apache and PHP7, then install them on Ubuntu 20.04 with:

sudo apt update

sudo apt install apache2 php7.4 libapache2-mod-php7.4

And install the following PHP extensions which are required by RainLoop.

sudo apt install php7.4-curl php7.4-xml

First, make a directory for rainloop in the current working directory.

mkdir rainloop

CD into the directory and download the latest RainLoop community edition with the following commands:

cd rainloop

curl -s http://repository.rainloop.net/installer.php | php

Once that’s done, move this directory to /var/www/.

cd ..

sudo mv rainloop /var/www/

Now set web server user (www-data) as the owner.

sudo chown www-data:www-data /var/www/rainloop/ -R

We can use either Apache or Nginx web server.

If you like to use Apache web server, then create the virtual host file with the following command:

sudo nano /etc/apache2/sites-available/rainloop.conf

Put the following text into the file. Replace red text with your actual info.

<VirtualHost *:80>
  ServerName mail.example.com
  DocumentRoot "/var/www/rainloop/"

  ErrorLog "/var/log/apache2/rainloop_error_log"
  TransferLog "/var/log/apache2/rainloop_access_log"

  <Directory />
    Options +Indexes +FollowSymLinks +ExecCGI
    AllowOverride All
    Order deny,allow
    Allow from all
    Require all granted
  </Directory>

  <Directory /var/www/rainloop/data>
     Require all denied
  </Directory>

</VirtualHost>

Save and close the file. Then enable this virtual host.

sudo a2ensite rainloop.conf

And reload Apache.

sudo systemctl reload apache2

If you want to add HTTPS to webmail, then you can obtain a free TLS/SSL certificate from Let’s Encrypt CA. First Let’s install the certbot client.

sudo apt install certbot

If you use Apache web server, then you also need to install the Certbot Apache plugin.

sudo apt install python3-certbot-apache

Then issue the following command to obtain a free TLS/SSL certificate. Replace the red-colored text with your actual email address and domain name.

sudo certbot --apache --agree-tos --redirect --hsts --staple-ocsp --email
 <font inherit/inherit;;#c0392b;;inherit>you@example.com</font>     -d
 <font inherit/inherit;;#c0392b;;inherit>mail.example.com</font>

Log into RainLoop admin panel via the following URL.

mail.example.com/?admin

Default username is admin and default password is 12345.

Once you are logged in, it’s recommended to change both your username and password since admin is an easy target. Click the security tab on the left pane. Update your password first, then re-login and update your username.

To access your emails through RainLoop, you need to configure email server settings in the Domains tab. By default, 4 email domains are added: gmail.com, outlook.com, qq.com, yahoo.com.

The SMTP server settings and IMAP server settings for these email domains are configured by RainLoop, but only Gmail is enabled by default. To enable the other 3 email domains, simply tick on the checkboxes.

To be able to access your own email server, click the Add Domain button and enter the IMAP and SMTP server settings of your own email server.

• IMAP: server mail.example.com, port 143, Secure STARTTLS.
• SMTP: server mail.example.com, port 587, Secure STARTTLS. Tick on Use Authentication.

If Rainloop and Postfix/Dovecot are running on the same server, then you can use the following configurations, so your server doesn’t have to look up the domain in DNS and establish TLS connection.

• IMAP: server 127.0.0.1, port 143, Secure None.
• SMTP: server 127.0.0.1, port 25, Secure None. Don’t use authentication on port 25.

You also need to enable your own email domain by ticking on the checkbox on the right, or the error domain is not allowed will appear when logging into your email address.

After finishing the configuration, enter your RainLoop webmail domain name in the browser address bar without /?admin suffix.

mail.example.com

And log into your email account.

RainLoop webmail

If authentication failed, then you may need to enable short login in the IMAP server settings page.

That’s all you need to do in order to access your emails on Gmail, outlook mail or your own email domain. If you add multiple email accounts, you can easily switch between them from the user drop-down menu. Very cool indeed! You can also configure other settings and customize your webmail interface.

By default, Rainloop will add a X-Mailer email header, indicating that you are using Rainloop webmail and the version number. You can tell Postfix to ignore it so recipient can not see it. Run the following command to create a header check file.

sudo nano /etc/postfix/smtp_header_checks

Put the following lines into the file.

/^X-Mailer.*RainLoop/   IGNORE

Save and close the file. Then edit the Postfix main configuration file.

sudo nano /etc/postfix/main.cf

Add the following line at the end of the file.

smtp_header_checks = regexp:/etc/postfix/smtp_header_checks

Save and close the file. Then run the following command to rebuild hash table.

sudo postmap /etc/postfix/smtp_header_checks

Reload Postfix for the change to take effect.

sudo systemctl reload postfix

Now Postfix won’t include X-Mailer: Rainloop in email headers.

If you use PHP-FPM to run PHP scripts, then files such as images, PDF files uploaded to Rainloop can not be larger than 2MB. To increase the upload size limit, edit the PHP configuration file.

sudo nano /etc/php/7.4/fpm/php.ini

Find the following line (line 846).

upload_max_filesize = 2M

Change the value like below. Note that this value should not be larger than the attachment size limit set by Postfix SMTP server.

upload_max_filesize = 50M

Then find the following line (line 694).

post_max_size = 8M

Change the maximum size of POST data that PHP will accept.

post_max_size = 50M

Save and close the file. Alternatively, you can run the following two commands to change the value without manually opening the file.

sudo sed -i 's/upload_max_filesize = 2M/upload_max_filesize = 50M/g' /etc/php/7.4/fpm/php.ini

sudo sed -i 's/post_max_size = 8M/post_max_size = 50M/g' /etc/php/7.4/fpm/php.ini

Then restart PHP-FPM.

sudo systemctl restart php7.4-fpm

Nginx also sets a limit of upload file size. The default maximum upload file size limit set by Nginx is 1MB. If you use Nginx, edit the Nginx configuration file.

sudo nano /etc/nginx/conf.d/mail.example.com.conf

Add the following line in the SSL virtual host.

client_max_body_size 50M;

Save and close the file. Then reload Nginx for the changes to take effect.

sudo systemctl reload nginx

Next, log in to the Rainloop admin panel (https://mail.example.com/?admin ) and change the attachment size limit.

Save the change. You need to log out from your webmail and log back in for the change to take effect.

Create a simple cron job to train SpamAssassin daily.

sudo nano /etc/cron.daily/spamassassin-learn

Now copy and paste this into the file

#!/bin/bash

# redirect errors and output to logfile
exec 2>&1>> /var/log/spamassassin.log

NOW=$(date +"%Y-%m-%d")

# Headers for log
echo ""
echo "#============== $NOW ==============#"
echo ""

# learn HAM
echo "Learning HAM from Inbox"
sa-learn --dbpath /var/lib/spamassassin/.spamassassin/ --no-sync --ham /home/*/Maildir/{cur,new}

# learn SPAM
echo "Learning SPAM from Spam folder"
sa-learn --dbpath /var/lib/spamassassin/.spamassassin/ --no-sync --spam /home/*/Maildir/.Spam/{cur,new}

# Synchronize the journal and databases.
echo "Syncing"
sa-learn --dbpath /var/lib/spamassassin/.spamassassin/ --sync

Important: The paths use glob (*) to scan ham and spam for all users (this only works if you trust all users to be sensible and move ham/spam to the right folder). It may affect your pi's performance. If you want to run on your username only, edit the paths so that they match your username!

Now make the script executable:

sudo chmod +x /etc/cron.daily/spamassassin-learn

sudo apt-get install dovecot-lmtpd

Edit /etc/dovecot/dovecot.conf Append this to enable lmtp:

protocols = imap lmtp

Edit /etc/dovecot/conf.d/20-lmtp.conf Add this line:

lmtp_save_to_detail_mailbox = yes

Now change the lmtp protocol block to look like this:

protocol lmtp {
  mail_plugins = $mail_plugins sieve
  postmaster_address = postmaster@yourdomain.com
}

Edit file /etc/dovecot/conf.d/10-master.conf Now find the service lmtp {… block and then change the line unix_listener lmtp {… to look like this:

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

Carefull with the open and close bracket { }

Edit file /etc/dovecot/conf.d/10-auth.conf and change:

auth_username_format = %Ln

Edit /etc/postfix/main.cf Comment out:

mailbox_command=

…and add:

mailbox_transport = lmtp:unix:private/dovecot-lmtp

Dovecot's sieve is already installed, you can check by running:

sudo apt-get install dovecot-sieve

Now we need to change one more parameter in /etc/dovecot/conf.d/90-sieve.conf

Uncomment this line:

recipient_delimiter = +

We still need to reload/restart Postfix and Dovecot to make that all the changes are loaded:

sudo service postfix reload
sudo service dovecot reload

The default place to put the sieve script is in the user's home folder: ~/.dovecot.sieve.

Note: You may need to repeat steps below for every user by replacing user in path for each username.

Create it like this:

sudo nano /home/user/.dovecot.sieve

and add this:

require ["fileinto"];
# Move spam to spam folder
if header :contains "X-Spam-Flag" "YES" {
  fileinto "Spam";
  # Stop here - if there are other rules, ignore them for spam messages
  stop;
}

Now chown the file to the owner of the mailbox, e.g.:

sudo chown user:user /home/user/.dovecot.sieve

sudo apt-get install dovecot-managesieved

open /etc/dovecot/dovecot.conf and add sieve to the protocols line:

protocols = imap lmtp sieve

and restart Dovecot:

sudo service dovecot restart

Finally, you must forward all the used ports for this implementation to your Raspberry Pi on your router:

• Mail Server: 443
• SMTP Server: 25
• IMAPS Server: 993
• SSMTP Legacy: 465
• Managesieve: 4190
• DKIM: 12301
• And possibly 110, 143, and 995

Viola!!! If everything is setup right you should have a fully functional email server at low cost. Enjoy your custom email!