Dovecot

This article describes how to set up a mail server suitable for personal or small office use.

Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written primarily with security in mind. Developed by Timo Sirainen, Dovecot was first released in July 2002. Dovecot primarily aims to be a lightweight, fast and easy to set up open source mailserver. For more detailed information, please see the official Dovecot Wiki.

Installation

Install the packages dovecot and pam from the official repositories.

Configuration

Assumptions

• Each mail account served by Dovecot, has a local user account defined on the server.
• The server uses PAM to authenticate the user against the local user database (/etc/passwd).
• SSL is used to encrypt the authentication password.
• The common Maildir format is used to store the mail in the user's home directory.
• A MDA has already been set up to deliver mail to the local users.

Create the SSL certificate

The dovecot package contains a script to generate the server SSL certificate.

• Copy the configuration file from the sample file: # cp /etc/ssl/dovecot-openssl.cnf{.sample,} .
• Edit /etc/ssl/dovecot-openssl.cnf to configure the certificate.

• Execute # /usr/lib/dovecot/mkcert.sh to generate the certificate.

The certificate/key pair is created as /etc/ssl/certs/dovecot.pem and /etc/ssl/private/dovecot.pem.

PAM Authentication

• To configure PAM for dovecot, create /etc/pam.d/dovecot with the following content:

/etc/pam.d/dovecot

auth    required        pam_unix.so nullok
account required        pam_unix.so 

Dovecot configuration

• Copy the dovecot.conf and conf.d/* configuration files from /usr/share/doc/dovecot/example-config to /etc/dovecot:

# cp /usr/share/doc/dovecot/example-config/dovecot.conf /etc/dovecot
# cp -r /usr/share/doc/dovecot/example-config/conf.d /etc/dovecot

The default configuration is ok for most systems, but make sure to read through the configuration files to see what options are available. See the quick configuration guide and dovecot configuration for more instructions.

By default dovecot will try to detect what mail storage system is in use on the system. To use the Maildir format edit /etc/dovecot/conf.d/10-mail.conf to set mail_location = maildir:~/Maildir.

Sieve

Sieve is a programming language that can be used to create filters for email on mail server.

• Install pigeonhole
• Add "sieve" to "protocols" in dovecot.conf (and the lines from the next points)

protocols = imap pop3 sieve

• Add minimal 80-sieve.conf

service managesieve-login {
  inet_listener sieve {
    port = 4190
  }
}

service managesieve {
}

protocol sieve {
}

• Add "sieve" to "mail_plugins" in "protocol lda" section

protocol lda {
  mail_plugins = sieve
}

• Specify sieve storage location in "plugin" section:

plugin {
  sieve=/var/mail/%u/dovecot.sieve
  sieve_dir=/var/mail/%u/sieve
}

Note: Nowadays it is recommended to use LMTP instead of LDA. Nevertheless can the Dovecot LDA still be used for small mailservers. More information can be found in the Dovecot Wiki

• Ensure that your MTA uses dovecot for delivery. For example: postfix's main.cf and dovecot-lda:

 mailbox_command = /usr/lib/dovecot/dovecot-lda -f "$SENDER" -a "$RECIPIENT"

Starting the server

Use the standard systemd syntax to control the dovecot.service daemon.

# systemctl start dovecot.service

To have it start on boot

# systemctl enable dovecot.service

Tricks

Generate hashes with non-default hash functions.

doveadm pw -s SHA512-CRYPT -p "superpassword"

Remember to make sure that the column in the database is large enough(you might not get a warning..)

Remember to set the password scheme in your dovecot-sql.conf file

default_pass_scheme = SHA512-CRYPT