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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>
[VirtualUsers.Home.txt]):

 * 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> [MailLocation.txt] to
system users' mail location and have the virtual userdb override it by
returning 'mail' <extra field> [UserDatabase.ExtraFields.txt].

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

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

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

dovecot-sql.conf.ext:

---%<-------------------------------------------------------------------------
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

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

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

dovecot-sql.conf.ext:

---%<-------------------------------------------------------------------------
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'
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2019-06-19 12:42)