I am having problems receiving email from certain domains. We seem to be receiving all email from other external domains just fine. Every test message that I send to myself is received instantly. We also have no problems sending email at all.
I noticed one thing, that if I watch the "Current Connections" in the Default SMTP Virtual Server I see a connection from that domain, but no one receives a message. Eventually the sender will get a bounce back that says the Connection Died.
I read of issues with EDNS and PIX Firewalls so I have tried disabling EDNS on my server, but that did not work. We are using a Sonicwall TZ 170 for our firewall.
Any suggestions of where to look or things to try would be very appreciated.