Setup:
We are running an Exchange 5.5 server sp4 on an IIS server. We have a firewall, which SMTP traffic is fully open on.
Problem: We are getting 400 and 500 series messages to other companies trying to email us. One of two things happens: One, the sending server says there is no response from mail host. But they can resolve our server name, and ping the server. Two, the sending server gets a deferred connection and it still never gets through.
I have tried to isolate what may be causing it for the past 8 WEEKS and have had no success. Most emails get through, but certain places/companies continually don’t with the reasons listed above. Any suggestions would be highly appreciated
