The process for migrating a BCS/CVS e-mail account to O365 is as follows.

At a predetermined day and time, several things will happen simultaneously:

Note that the process of migrating your data to O365 may take a considerable amount of time...more than a day for the larger IMAP users.

Once this process begins, you now need to modify your e-mail client(s) so you can start using O365. This means adding the O365 account to each client.

Instructions for adding an O365 account to Thunderbird using the IMAP protocol are here: O365ThunderbirdImap

Instructions for adding an )365 account to Thunderbird using the POP protocol are here: O365ThunderbirdPop

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