Some outside users trying to send messages in are getting this dreaded bastard:
The e-mail account does not exist at the organization this message
was sent to. Check the e-mail address, or contact the recipient
directly to find out the correct address.
I've searched and searched, and made sure of everything that everyone else suggested (smtp policy is correct for my domain, only one mx record)...I even did the MS suggestion of disabling the "exchange handles all email for this domain" thing...it just started doing this and has been working fine. Our emails are routed from an outside email: firstname.lastname@example.org is hosted by our ISP, but that is then forwarded to email@example.com for internal Exchange use. I have an smtp entry for both blah.net and blahblah.com in the policies (should that be like that), but still, crap.
Some emails get through, some don't (the notification from experts-exchange happens to be one of the ones that doesn't get through). I've checked our servers at dnsreport and all is reportin fine.
Any ideas? Everything was working fine and then poof :)