Postby BaldBoy » Sat Oct 23, 2010 11:36 am
It could be no fault from your users.
Scalix's MTA accepts every incoming message and only when it's in the queue it decides if the recipient exist or not. If the recipient does not exist then it delivers a non-delivery report message to the sender. Scalix's MTA does not reply with a 550 error for unknown addresses during the smtp session.
As spammers mostly send messages to any kind of address inside a domain it always happens that your scalix server tries to contact senders (in 99.9% of cases with non luck) to say that mailbox does not exist.
I'd suggest you the reading of this thread
http://www.scalix.com/forums/viewtopic.php?f=23&t=12513