I'm in the process of migration from Exchange 2007 to Office 365.
It is going to be a slow migration, so I need to maintain both environments running.
What I've done for the first "migrated" mailboxes is to create the account at Office365, then create a redirection from Ex2007 to O365 using the .onmicrosoft.com email, which is the secondary smtp address.
It works properly for sendings and receptions, so using OWA or laptops outside domain is good.
The problem comes with Outlook installations inside domain.
I can't manage Outlook to look Office365 for connection. It always finds the Ex2007 user and establishes connection to it. I've done the trick of deleting primary SMTP address on Ex2007, establish connection to Office365 (it has worked) and after this, re-establish primary SMTP address to what it has to be (same address as O365), and after a couple of day, it again disconnects from ExOnline and looks to Ex2007.
How do you think I could manage this? Could I stablish a non top priority MX record pointing to O365 and the delete user from Ex2007, so that if email looks to Ex2007 and doesn't find it, retry to second MX record and find it at O365?
Please, any help would be great!!