Thank you I'll give it a try......I had configured 0.0.0.0 refused for MercuryS, but I was getting a ton of Delivery Failure bounces for one particular user and I wasn't sure if there was something I was missing.  I'll go ahead and change it to your suggestion and see what happens.  Anything else one can do for the Delivery Failure bounces?  They're not usually this much of a problem, but this time it's a real pain!

Newbie here.....I'm using Mercury v4.0.1b which I will update to v4.52 ASAP and modules MercuryS, C, & P in a Win2k domain environment.  How do I lock down my mail server to only receive mail from a particular IP range (from my mail filtering service) and thereby block anything sent directly to my MX server?

 Thanks

Go to Configuration | MercuryS | Connection control and use allow to set the IP addresses you want to receive mail from and then set a refuse of 000.000.000.001 to 255.255.255.255.