• Authentication
• MultipleDatabases

Multiple Authentication Databases

Dovecot supports defining multiple authentication databases, so that if the password doesn't match in the first database, it checks the next one. This can be useful if you want to easily support having both local system users in /etc/passwd and virtual users.

Currently the fallback works only with the PLAIN authentication mechanism.

Often you also want a different mail location for system and virtual users. The best way to do this would be to always have mails stored below the home directory (virtual users should have a home directory too):

• System users' mails: /home/user/Maildir
• Virtual users' mails: /var/vmail/domain/user/Maildir

This can be done by simply having both system and virtual userdbs return home directory properly (i.e. virtual users' home=/var/vmail/%d/%n) and then set mail_location = maildir:~/Maildir.

If it's not possible to have a home directory for virtual users (avoid that if possible), you can do this by pointing mail_location to system users' mail location and have the virtual userdb override it by returning mail extra field.

Example with home dirs

• System users' mails: /home/user/Maildir
• Virtual users' mails: /var/vmail/domain/user/Maildir

dovecot.conf:

# Mail location for both system and virtual users:
mail_location = maildir:~/Maildir

auth default {
  mechanisms = plain

  # try to authenticate using SQL database first
  passdb sql {
    args = /etc/dovecot-sql.conf
  }
  # fallback to PAM
  passdb pam {
  }

  # look up users from SQL first (even if authentication was done using PAM!)
  userdb sql {
    args = /etc/dovecot-sql.conf
  }
  # if not found, fallback to /etc/passwd
  userdb passwd {
  }
}

dovecot-sql.conf:

password_query = SELECT userid as user, password FROM users WHERE userid = '%u'
user_query = SELECT uid, gid, '/var/vmail/%d/%n' as home FROM users WHERE userid = '%u'

Example with overriding mail location

• System users' mails: /home/user/Maildir
• Virtual users' mails: /var/vmail/domain/user

dovecot.conf:

# the default mail location for system users, this will be overridden in userdb sql.
mail_location = maildir:~/Maildir

auth default {
  mechanisms = plain

  # try to authenticate using SQL database first
  passdb sql {
    args = /etc/dovecot-sql.conf
  }
  # fallback to PAM
  passdb pam {
  }

  # look up users from SQL first (even if authentication was done using PAM!)
  userdb sql {
    args = /etc/dovecot-sql.conf
  }
  # if not found, fallback to /etc/passwd
  userdb passwd {
  }
}

dovecot-sql.conf:

password_query = SELECT userid as user, password FROM users WHERE userid = '%u'
# returning mail overrides mail_location setting for SQL users.
user_query = SELECT uid, gid, 'maildir:/var/vmail/%u' as mail FROM users WHERE userid = '%u'