Dovecot

Dovecot is an IMAP and POP3 server, and is used on Wikimedia's IMAP server sanger.

Dovecot can be installed from the Ubuntu dovecot-imap package, which also pulls in dovecot-common.

Configuration

The configuration file resides in /etc/dovecot/dovecot.conf. Dovecot has very reasonable defaults, so not many settings need to be changed.

We only support IMAP over SSL/TLS:

protocols = imaps

As we have a unified virtual users IMAP setup, the Maildir directory can be determined using a template:

mail_location = maildir:/var/vmail/%d/%n

The Ubuntu default configuration has group mail added by default; this is not needed in our configuration.

#mail_extra_groups = mail

When copying a message, do it with hard links whenever possible. This makes the performance much better, and it's unlikely to have any side effects.

maildir_copy_with_hardlinks = yes

Restrict allowed UIDs to be used for accessing mail to precisely the vmail UID:

first_valid_uid = 107
last_valid_uid = 107

We use PLAIN authorization using a SQLite password database, and static user info mapping:

auth default {
  mechanisms = plain

  passdb sql {
    args = /etc/dovecot/dovecot-sql.conf
  }

  userdb static {
    args = uid=107 gid=112
  }
}

Details of SQL queries are specified in the file /etc/dovecot/dovecot-sql.conf.

We're using SQLite:

driver = sqlite
connect = /var/vmaildb/user.db

The default password hashing scheme is Salted SSHA-1:

default_pass_scheme = SSHA

To obtain the password field for a given username, the following SQL query is used:

password_query = SELECT localpart||'@'||domain AS user, password FROM account WHERE localpart='%n' AND domain='%d'

Escaping of the username is handled by Dovecot, see the main configuration file.