Best way to migrate large IMAP mailboxes to Microsoft 365?
I'm working on an IMAP-to-Microsoft 365 project involving several fairly large mailboxes. The initial migration works, but as the mailbox size increases, I'm seeing migration batches take much longer and occasionally finish with skipped folders or missing items.
Microsoft's own troubleshooting material acknowledges that IMAP migrations can encounter missing folders and missing individual items.
For anyone who has dealt with this, what is your preferred approach to Migrate IMAP to Office 365 for larger mailboxes? Would you continue retrying the native migration batches, or move to a dedicated migration utility?
I came across the DRS Softech IMAP to Office365 Migration Tool, which supports bulk mailbox migration, date-based filtering, incremental migration, and large mailbox transfers. The ability to migrate only a selected date range could be useful for testing before moving an entire mailbox.
I'm mainly looking for practical experience here. Did using a third-party tool actually reduce skipped items and migration failures, or did you eventually resolve the issues with Microsoft's native migration?
Rohit Patwa
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