Migrating hosted exchange to O365

[Aaron1035]

Hello, We are in the process of migrating our third party hosted exchange to O365 and the issue I run into is when I upgrade the license to E3 users receive security credentials box for Outlook. Is there a work around or is it because of auto-discover in O365 it can't find the user credentials since we are in a hosted environment?

[#2]

when you assign the E3 license to a user it is actually creating a mailbox for them in O365, and so if your autodiscover record was changed to point to O365 then that prompt is expected. Best practice is to wait to change autodiscover until you migrate all your email data and you are ready for the email cutover event (changing MX record too).