Can I migrate Microsoft 365 mailboxes without losing emails or attachments?

Yes, you can migrate Microsoft 365 mailboxes while preserving emails and attachments, provided the migration is properly configured and the source data is supported. Microsoft’s cross-tenant mailbox migration transfers user-visible mailbox content, including emails, contacts, calendars, tasks, notes, and Recoverable Items. For a more controlled migration, the SysInfo Microsoft 365 Tenant to Tenant Migration Tool supports mailbox mapping, incremental migration, duplicate removal, date-range filtering, and attachment handling. It can migrate emails with attachments or exclude attachments when required to reduce mailbox size. The tool also uses OAuth 2.0 authentication and TLS-encrypted HTTPS for secure data transfer. However, no migration method can guarantee every item will migrate if the source contains unsupported or corrupted data. Microsoft specifically notes that corrupted items and certain unsupported mailbox content may not migrate. Therefore, it is recommended to test the migration with a demo or pilot batch and verify the migrated mailboxes before completing the full transfer.