I have an issue right now. We are migrating to office 365 but we've only done a few users for testing. The rest of the users are still on the local exchange 2010 server. Recently we added a new user mailbox to the local exchange server but when we try to send email to that account it returns with a:
The email address wasn't found at the destination domain. It might be misspelled or it might not exist any longer. Try retyping the address and resending the message.
If that doesn't work, contact the recipient (by phone or instant messaging, for example) to check that the address is correct. If the problem continues, forward this message to your email admin.
For Email Administrators
For more tips to help fix this issue, see DSN 5.1.1 Errors in Exchange Online and Office 365.
I take a look at the mailbox and I see that it has no X400 address at all. It has 2 SMTP address, one to office 365 and one to our domain. The system is expecting the mailbox to be in office 365.
How do I fix this? I need this new local mailboxes to be reachable locally as well as those in office 365