Email migration step-by-step

In TheMigrator → New migration, select Email as the migration type. Select your source tenant and destination tenant.

TheMigrator auto-matches mailboxes by username prefix (the part before @). Review the mapping table and fix any mismatches. Mark any mailboxes you want to skip.

• Green rows: auto-matched by prefix — verify the destination address is correct.
• Yellow rows: unmatched — enter the destination email address manually or mark as skip.
• You must resolve all unmatched mailboxes before continuing.

Choose which items to include: Email is always included. Toggle Calendar and Contacts based on your requirements. Most full migrations include all three.

Select Start immediately to begin now, or set a scheduled start time. For large tenants (500+ mailboxes), scheduling overnight avoids competing with business-hours Graph API usage.

Enabling Dry run validates all mappings and estimates item counts without moving any data. Recommended for first-time migrations or tenants over 200 mailboxes. A dry run typically completes in 10–20 minutes.

Review the summary and click Launch migration. Monitor progress in the job detail view — per-mailbox progress, item counts, and error logs are updated in real time.

• A healthy migration shows a steady increase in items migrated per minute.
• Throttle warnings (429 errors in the log) are normal — the worker retries automatically.
• Persistent errors on a single mailbox usually mean a permissions issue or a corrupt item — check the error log for details.

24–48 hours before DNS cutover, run a second migration pass on the same job. TheMigrator will only migrate items created or modified since the initial sync. This dramatically reduces the cutover window.