Outbound e-mail to transferred domain still being routed internally

[StefIsScared]

As a result of our company's expansion, we've recently split to two companies on two sites. Two of our domains and three of our accounts have been moved to a new server. The MX records have been altered accordingly, the old accounts have been deleted from our old server and the domains in question have been disabled and now deleted in the exchange recipient policy.

Emails are sending to these accounts OK from external email addresses, such as webmail accounts or those of clients, but when we try to send from our server here, it seems to always route the email internally. Now that I have deleted the mailbox, it seems to be stripping the domain, replacing it with our primary domain, then bouncing it as the mailbox no longer exists.

Now here's the really weird thing... it was working last week and we haven't changed anything over the weekend. But it gets stranger still, immediately after deleting one user's mailbox, I sent an e-mail which got through, but when I replied to his confirmation that he had received it, my email got bounced as described before. I checked that his reply-to address wasn't the problem and this is set as the address I originally sent to.

There is also one user whose account is reportedly not malfunctioning, but it may be suffering the same intermittent malfunction.

All very strange. Hope someone can help.

Thanks

 

[StefIsScared]

Interesting development on this one. It seems that e-mails are getting through, but that the server here is returning an undeliverable report anyway, so presumably it is now trying to route internally, failing, then trying to route externally.

Any ideas how to stop this?