Here's the scenario: Company A has a Windows 2003 domain with their own Exchange 2003 server. email domain is companya.com Company B is a subsidiary of a much larger company. They have their own windows 2000 domain server and got their email through the exchangeb server of their parent company. email domain is companyb.com Company A aquires Company B, but wants to conmtinue letting run as a separate entity. Company B keeps their domain server, but now gets their email through Comnpany A's Exchange server (they were setup as a separate OU in AD). MX record was changed to point to company A's Exchange server. This all occurred several weeks ago, and all has been working fine - ALMOST! It seems that randomly, some email messages (new and replies) meant for a companyb user is bounced back to the sender with a message that the recipient does not exist (but it does). The interesting part is that just below that bounceback message is referenced company B's old email servername. It's as if some random messages are getting routed to company B's old server. The MX record is correct and it's been several weeks, so I would expect all DNS servers to be up-tp-date. Running a DNS report at dnsstuff.com does not show any problems (just a warning about not having an SPF record). Any suggestions on how to troubleshoot this? Post #: 1

Is there any similarity amongst the senders that are getting messages bounced? From the same company, same mail provider, etc... On a sender that messages bounce from, do they always bounce for that sender or do they sometimes get through? I doubt a MX record could get that stale in DNS since we're talking about a couple of weeks. Is there any chance that somewhere out there there is a mail system that is setup with a connector that routes mail for companyb.com directly to the old mail server instead of routing it via MX record lookup in DNS? A copy of the message headers from the bounced message would also be handy to help identify the mail servers it traversed on its way to the out companyb mail server.

F.Y.I. I think we found the problem.Turns outit was mostly a problem with mail coming from one domain. Upon further investigation, that domain used to be a sister company of company B, so they are using the same mailserver that company B was using before they were purchased by company A. So somewhere on the senders domain, there must still be references to company B as being on their local network, which it is not, hence the bouncebacks. It will be up to them to fix that, but I'm sure we have found the cause. Thanks to all. Al