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Another Exchange Question about system Undeliverable

Hello everyone.  This is only my second time posting, but I have been wrapping my brain around trying to find a solution to this problem. I have Exchange 2003 and some of my users have been getting undeliverable. I have scowered this site and couldnt find someone with the same problem as me, but this is what we get.

 There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <mail.ppmco.com #5.5.0 smtp;550-mailinc25: Host <Our IP Address is here for our firewall>: No email accepted from this host>

The IP address is the IP address of our Firewall.  Its our external address. We dont get this on all emails, just certains domains that we send too.  I have already done an nslookup and have looked at dnsstuff.com. All appears to be ok. We do use appriver.com as our filtering. All emails that go external are routed through appriver, then out. Vise-Versa for when mail comes in. Any clues or help would be appreciated!! :P

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1 Solution
Sounds like it could be a few things, such as;

Blacklisted IP Address - do a spam database lookup on dnsstuff
No Reverse DNS Entry - do a reverse dns entry lookup on dnsstuff

There could be more there to do with configuration, but I would check out the obvious stuff first

woohahAuthor Commented:
Well, I did check the Reverse DNS entry and it looks like it resolves. We dont appear to be blacklisted either. Im clueless! :(
It isn't an Exchange message.
Do you know who is rejecting the message?
If you are routing email out through the service provider, then it might be one of their servers that is rejecting the message. Have you got message tracking enabled? Does that show the NDR being generated?

woohahAuthor Commented:
I have no clue who is rejecting the message and I do not have message tracking enabled. I guess I should enable message tracking and take a look if the NDR is being generated from that. I will try it and see.

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