This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

Passwd

User is looked up using getpwnam() call, which usually looks into /etc/passwd file, but depending on NSS configuration it may also look up the user from eg. LDAP database.

Most commonly used as a user database. Many systems use shadow passwords nowadays so it doesn't usually work as a password database. BSDs are an exception to this, they still set the password field even with shadow passwords.

The lookup is by default done in the auth worker processes. If you have only a small local passwd file, you can avoid having extra auth worker processes by disabling it:

userdb {
  driver = passwd
  args = blocking=no
}

Field overriding and extra fields

It's possible to override fields from passwd and add extra fields with templates. For example:

userdb {
  driver = passwd
  args = home=/var/mail/%u mail=maildir:/var/mail/%u/Maildir
}

This uses the UID and GID fields from passwd, but home directory is overridden. Also the default mail_location setting is overridden.