I am transferring a small office from Microsoft Exchange to Office365. I would like to set up all the users and transfer all their email before we go live. I have added all the specified records to the DNS with the exception of the MX record, so mail is still being delivered via the "on premises" Exchange Server. When setting up the users I have a choice of using the "tenant domain" username@...onmicrosoft.com or the actual company Domain Name. Initially I tried to use the actual company domain name on one computer running Outlook 2010 but ran into a lot of problems with it repeatedly requesting logon details. So am now unsure what is the correct method of doing this, should I use the tenant account to set up the mailboxes,upload old emails and set up Outlook and then change over to the actual company domain name one the MX record has been changed or should I always use the actual company domain name for this ? I have the impression that using the same domain name in the "on premise" server and the office 365 both on the same computer user caused the problem but I cannot be sure.
Any assistance or reference to guides on the best way of doing this would be appreciated