Migration from Hosted Exchange 2010 to Office365

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hopefully I can get some ideas for a migration of a customer with 250 email accounts by the end of january. We are a small MSP provider and the idea is to migrate from a Hosted Exchange 2010 server (we do not have any admin rights so migration tools will be really difficult) to Office 365 and Cisco Email Security Cloud Version.


Right now all users connect with their email information, so the dont use their domain.


Some weeks ago we did some testing (also with smaller clients with the same environment) and we had a pretty good concept that worked just fine but after testing last week it is not possible anymore:


1.Changed actual email configuration on the HostedExchange from test@abcd.com to test@abcd.my-hosted-exchange.com - same credentials to login

2. Created the O365 User and changed the domain parameters (autodiscover, etc.)

3. In the same Outlook profile we attached a new email and with the new autodiscover it was really easy and fast to integrate the new email to the existing profile. So by that we would have all the old Outlook configuration and the user would have access at the same time to his old email (he would receive new information but could check and import importante information). Basically the most important thing was that Outlook seemed the same for the user and so he would have auto completation while creating new emails, etc. Some user we would also import the old PST file to have almost all data from the HosetdExchange email.

4. After one months we would delete the old HostedExchange Email and the user only would have to delete it in his Outlook.


Problem now is that we were testing the same and now Outlook doesnt let us create the new O365 Email and we get a message that the email test@abcd.com already exists, even though we changed to teh O365 and alkl domain issues. It is like the old name is "cached" and so we cannot process the same way.


Any good ideas how we can perform this change the best way?


Thanks for your input!


1 Reply

Best use the default @tenant.onmicrosoft.com address you are given when you create a mailbox in O365.