auth.conf was always written, even if no username/password provided.
In this case only the ip or Hostname of the mailserver was written into
auth.conf. Now the file is only filled if username/password are filled.
Signed-off-by: Alexander Marx <alexander.marx@ipfire.org>
Tested-by: Timo Eissler <timo.eissler@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
