I’m planning a Microsoft 365 migration for an organization with multiple Exchange users, and each user has an archive mailbox containing historical emails. Handling one mailbox isn’t particularly difficult, but I’m trying to understand how administrators manage the process when there are many users.

The main requirement is to Migrate Archive Mailbox to Microsoft 365 while keeping the data organized and ensuring that each archive is transferred to the correct Microsoft 365 account. User mapping therefore seems to be an important part of the process.

I’m also concerned about duplicate data. Some mailboxes may have already been partially migrated, so restarting the entire process could result in unnecessary transfers. Having options for filtering emails by date and skipping previously migrated data would make the process easier to manage.

I came across SysInfo Office 365 to PST Export Tool while researching third-party solutions. It provides user mapping along with date filtering, duplicate removal, skip-previously-migrated-data, and migration reporting features. These could be helpful when dealing with multiple archive mailboxes instead of processing every user individually.

For administrators who have completed a multi-user Exchange archive migration, how did you organize the project? Did you migrate users in batches, and how did you handle failed or interrupted migrations? I’d also like to know what method you used to confirm that every user’s archive data reached the correct Microsoft 365 mailbox after the migration.