As has been mentioned in this list before, using that option violates the RFCs. It prevents bounce messages from getting sent to your users, and is considered rude. The problem is that when those bounce messages aren't accepted, they get bounced to the postmaster on the remote domain, who shouldn't have to deal with them.

Because this is getting to be such a problem, there is now a web site www.rfc-ignorant.com that is starting a new DNS-based test (like RBL, RSS, DUL, and ORBS) that can let administrators decide to block E-mail coming from your users. FYI, we have already added support in Declude for this type of test ("rhsbl"; it looks up the domain name on the right hand side of the "@" sign in an E-mail address).

So, if you have "Refuse NULL <> Senders" checked on the SMTP Security tab of IMail Administrator, it's time to uncheck it.

-- -Scott

Declude: Anti-virus and Anti-spam solutions for IMail. http://www.declude.com --