Resolution
If you found that your server acts as open relay, please check the following:- Check relaying setting on the "Server-wide mail preferences" page at Server->Mail page in Parallels Plesk Panel. It should be set to "authorization is required".
- Make sure that there are no unwanted IPs/Networks in white list on the Server->Mail->White List in Parallels Plesk Panel. By default this list should contain only "127.0.0.1 / 8" or "127.0.0.1 / 32". This record means that authorization is not required only for one IP 127.0.0.1. It is done to allow mail sending from Webmail.
- Check that SMTP is served by Plesk Qmail but not another software, see article 1837.
If the server was open relay for a long time, most probably it is flooded with SPAM. Check how many messages in queue using "$QMAIL_ROOT_D/bin/qmail-qstat". If queue contains too many messages see article 766.
Keywords: open relay relaing everyone can send mail without authorization spam