Hi,
We have a mail server running Exchange 2013 in hybrid mode. We have migrated all mailboxes to Office 365 with no problems.
However, when new user accounts have been created, they are unable to recieve external email. The accounts are on Office365, but the NDR that we recieve is generated by our exchange server.
The message in the NDR is "Remote Server returned '420 4.2.0 Recipient deferred because there is no Mdb'"
This user can send emails to external accounts, and these emails come from username@domain.com
I can send an email from an external account to this user by emailing username@domain.onmicrosoft.com, it is only when using username@domain.com that I recieve this NDR
Any help would be greatly appreciated.