#5.5.0 There was a SMTP communication problem with the recipient's email server smtp: No email accepted from this host
Posted on 2006-11-01
Perhaps someone can help me with this. We have no trouble receiving external email. But we are receiving the above NDRs on some, but by no means all, of the domains to which our Server 2003 SP1 Exchange 5.5 sends email. That is if the email ever makes it off the server, which I suspect many don't. Certainly the Queue in Exchange shows many stuck there, generally with the message "SMTP could not connect to any DNS server".
At least 2 of the unreachable recipients have white listed our company. We are only blacklisted as an open-range address at SORBS, which I cannot fix as the IP addresses listed belong to our ISP. Our Active Directory in Server 2003 was set incorrectly, specifying .net as the default SMTP address instead of .com, but I have fixed that. Recipient policy is also @.com, I have unchecked .net .
Our mail server is mail.pfgoptics.com and is hosted by a third party provider, not our ISP. But our POP 3 connectors list the correct mail server address, and are having no problem retrieving email. Our Default SMTP connector uses DNS. I have changed the FQDN in the virtual SMTP server to both mail.pfgoptics.com and mx.pfgoptics.com, and probably every other variation you could think of, to no avail. I have done the same with our internal MX record. If you search on that at dnstuff.com, it comes up with mx.pfgoptics.com, rather than mail.pfgoptics.com, as our mail server, I have tried to reflect that in DNS but no combination works thus far …
I have also tried creating a separate SMTP connector using the ISP mail.pfgoptics.com address instead of DNS, listing the problematic sites and applying reasonable costings, also to no avail. As emails were now showing a valid domain as unreachable, I deleted that. Also DNS related, I have checked that both the internet NIC and the Internal Network NIC reference the internal network address only for DNS. The Internet NIC uses a static IP address, not DHCP.
I have opened port 25 on the firewall to all protocols, SMTP not being listed explicitly, but, also no joy. Adding a filter enabling SMTP also does not help.
I have run the Internet connectivity wizard twice - which necessitated restoring AD entries back to .com for SMTP afterwards - but did not fix the problem.
The elephant is the room is that, after fixing Active Directory entries, most sites were receiving, but upgrading our anti-spam software to enable real-time blacklists appears to have broken something again. White listing domains there was no help, nor was removing RBL protection, which I turned back on. I also stopped the anti-spam software, which has not improved the situation.
Any help would be most appreciated. I am offering 500 points as I have been banging my head on the server door for far too long now!