Аутентификация средствами dovecot

Проверка, включена ли поддержка аутентификации dovecot:

# exim -bV | grep Authenticators
Authenticators: dovecot

Если поддержки нет, тогда пересобрать:

.if ${.CURDIR:N*/usr/ports/mail/exim} == ""
...
ваши опции
...
WITH_AUTH_DOVECOT=YES
.endif

Настройки секции аутентификации в Exim:

begin authenticators

auth_plain:
  driver = dovecot
  public_name = PLAIN
  server_socket = /var/run/dovecot/auth-client
  server_set_id = $auth1

auth_login:
  driver = dovecot
  public_name = LOGIN
  server_socket = /var/run/dovecot/auth-client
  server_set_id = $auth1

auth_cram_md5:
  driver = dovecot
  public_name = CRAM-MD5
  server_socket = /var/run/dovecot/auth-client
  server_set_id = $auth1

Настройки dovecot (выделено):

auth default {
  mechanisms = plain login cram-md5
  socket listen {
    master {
      path = /var/run/dovecot/auth-master
      mode = 0600
      user = mailnull
    }
    client {
      path = /var/run/dovecot/auth-client
      mode = 0660
      user = mailnull
    }
                }

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

  userdb sql {
    args = /usr/local/etc/dovecot-sql.conf
  }
  user = root
}

Читать:
/usr/local/share/doc/dovecot/wiki/HowTo.EximAndDovecotSASL.txt