We have been running exchange 2007 for almost two years and I've been having this problem off and on for a while. For some reason our exchange cannot send attachments larger than 1mb to a handful of domains. The emails get hung in the queue with error "421 4.4.2 Connection Dropped" Here's what I've done so far...
Checked Check Point firewall logs...nothing
Ensured certificates are not expired
I can telnet to port 25 on the mail servers in question and send helo commands
Tried disabling trend mailscan on smtp server
Tried disabling trend officescan on smtp server
If I send the same attachments from Gmail to the problem servers, it goes through
If I send the same attachments from my exchange to my gmail, it goes through
called the receiving party and made sure my ip address and domain are whitelisted on their spam filters
used mx toolbox to ensure my domain is blacklisted anywhere
I've seen other posts talk about a TCP offload engine setting for the NIC, however I'm running a Dell Poweredge 1950 with Broadcom BCM5708C NetXtreme II and I don't see any such setting for my NIC. I think this is related to HP servers only.
Please throw me a bone here...I'm about to start pulling out my hair!!