Ever since migrating to SBS2011, we have some (2-3) clients that have serious delays when sending us mail with attachments. The attachments are just PDF/DOC files, and aren't large or malware containing.
We're running latest SBS2011 + SP/Security fixes/rollups for Exchange 2010.
The clients are large, some of them send to tens of thousands of domains a day.
We get about 1-2K messages a day fine from most domains. We have a fairly good pipe at 20/20 Mbps. It's never saturated.
This started after we migrated from Exchange 2003 on Server 2003 to Exchange 2010 on SBS 2011.
We have zero issues from the vast majority of domains, nor do we have issues sending to these 2-3 domains.
We run a Watchguard Firewall (NAT) but I've followed their best practices and tweaked everything I can think of.
We have difficulty getting the admins of these domains to help us. We're small potatoes to them.
Any ideas? I've tried changing some of the tarpitinterval, MaxInboundConnectionPercentagePerSource, MaxInboundConnectionPerSource, settings, but at this point I just want to turn it all off to see if it's related.
no