Many organization utilize Exchange Online Protection (EOP) for their on-premises Exchange mail scrubbing and filtration. The question becomes, what to do when you want to transition your EOP from on-premise and convert to cloud only mailboxes.
The answer might surprise you.
1. Pointed MX back at on premises server. Waited 2 hours.
2. Disabled Standalone EOP connector. THIS IS THE CRITICAL step!! Waited one hour.
3. Purchased EXO licenses, wait 30-60 minutes, for Exchange online to provision. Do NOT purchase licenses before Step (2) !
4. Setup a cutover migration – it will auto-create all the user/mailboxes in under an hour.
5. Licensed and logged into Outlook web
6. Changed MX back to O365
(Cut-over migration is still running fine)
MS needs to address this. Some many people on Stand alone EOP are going to get burned by this.
For more information read this thread: http://community.office365.com/en-us/forums/156/p/178192/708536.aspx?wa=wsignin1.0