#​7. Perform the final cutover

​Modify Exchange MX records, etc. It can take up to 72 hours (related to the TTL mentioned in the previous section) for your email systems to recognize the changed MX records. We recommend you run a final incremental job after the cutover to ensure updates of source data are migrated to the destination. Make sure the source email addresses in project mappings are not modified, and the destination email addresses in project mappings exist as aliases of the original destination email addresses.

*Note: If you have run a full or incremental migration job for mailboxes and then changed the prefixes or domain names of mailbox addresses in the source or destination tenant (for example, you have migrated userA@src.com to userA@dest.com and then changed the source tenant domain name from src.com to newsrc.com), the subsequent migration jobs (full or incremental jobs) will not fail even if you do not change the prefixes or domain names of source or destination email addresses configured in project mappings. This is because Fly now uses mailbox IDs to migrate mailboxes.