We have recently begun a migration to office365 from Exchange 2003.
We have started a staged migration and moved two users from on-premise to the online exchange.
I have configured DirSync and all is working with that and I have migrated the two users mailboxes over to Outlook online using Outlook Anywhere endpoint and all is ok here.
The issue we have now is that the two users who have been migrated can send email externally and users on-premise can send email to them however the two users cannot send emails to the users on premise.
After some research I wondered if:
We need to setup a server runing exchange 2007 which allows routing back to exchange 2003
I can setup a form of routing within online exchange to send the emails back to on-premise for delivery
We have no other users migrated over, although they are ready to be moved.
The error the two migrated users receive can be different for different recipients. It is either:
Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound
; Recipient not found by SMTP address lookup'
Remote Server returned '< #5.2.1>'
I have looked at other posts on here and I have seen the use of the NK2Edit application to remove X500 address as it will be using the legacy exchange information but this has not resolved the issue.
Any help would be gratefully received.