This is a continuation of http://community.office365.com/en-us/forums/160/p/64660/247836.aspx#247836
Emails from (at least one) external domain do not get through to my O365 domain (or the onmicrosoft.com address), do not show under OWA Delivery Reports, and the sender gets no immediate notification of any error. Eventually the sender receives a permanent "Mail delivery failed: returning message to sender" error, although no useful information is sent with the error so I just get a "retry timeout exceeded".
The error is definitely at the Exchange Online end. To verify this I set up a distribution group group@domain.com with just one member me@domain.com. I sent a mail from the external email address to group@domain.com and eventually (after about 6 days) got the following error:
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
me@domain.com
(generated from group@domain.com)
retry timeout exceeded
Thus Exchange Online is resolving the distribution group ok but failing with the actual user email address for some unknown reason.
Cheers
-- Mike --