Exchange 2003: SMTP Auth, Spam and RBLs - How to allow legit email
Posted on 2010-09-02
Server = Exchange 2003 and Symantec Mail Security using RBL to reject 'known' spammers. Server is NOT an open relay.
Last week we had a compromised email account used to relay spam through our corporate server. The spammers properly authenticated to the server, so the relay was allowed. I had everyone change their password as a precaution.
I have remote users that use broadband from home, hotels and such that cannot connect to our mail server if their originating IP is on the RBL. If I add an exception to allow all email accounts from @ourdomain.com to bypass the RBL, then we are exposed to a degree I am not comfortable with.
I have considered using a non traditional port number for them to send email to our server with a firewall proxy exception to allow all @ourdomain users to bypass the RBL, but I haven't been able to get it to function reliably.
Can anyone recommend a good solution for allowing authenticated users to access our server from RBL listed IP addresses that won't expose us unnecessarily to spamming risks?
I hope this makes sense. I'm happy to clarify anything as needed.
Thanks in advance for your help.