One thing I don't see discussed enough is what happens to new emails while the migration is running. Employees obviously continue receiving and sending messages, so stopping mailboxes for several hours isn't an option.

We're planning to Migrate IMAP to Office 365 in stages and want to move historical mail while keeping the source mailbox available until the final cutover. Ideally, we also want to avoid importing the same messages repeatedly when running another migration pass.

I've been looking at the DRS Softech IMAP to Office365 Migration Tool because its incremental migration feature appears useful for this type of situation. If the initial batch transfers older data, an incremental pass could potentially help bring over newer messages without unnecessarily duplicating everything.

For admins who've done this before, how did you structure the migration? Did you perform a full initial migration followed by an incremental pass before changing DNS, or did you use Microsoft's native synchronization until the cutover?

I'd also appreciate advice on how you verified that the final mailbox contained everything before shutting down the old IMAP service.

Read the Complete Blog - https://www.drssoftech.com/blog/imap-to-office-365-migration/