Know what an MX change affects
An MX record tells other mail systems where to deliver new messages for your domain. After a change takes effect, incoming mail is routed according to the published records and their priorities. Messages already delivered remain in the mailbox or archive where they were stored.
Changing routing and moving mailbox data are separate tasks. If you switch providers, plan both: update the destination records and separately export or migrate existing messages, folders, contacts, and any account settings you need. Do not assume that pointing the domain to a new service transfers historical mail.
Plan a mail provider transition
Before changing records, check the new provider's required MX values and any verification steps. Keep a copy of the current DNS configuration, and coordinate the change with mailbox setup so the destination accounts exist before new mail begins arriving there. A transition without prepared mailboxes can interrupt delivery.
After updating the authoritative DNS zone, verify the records and send a test from an external address. Continue checking both providers during the transition window, since caches and message delivery can take time to settle. Confirm that historical mail is present in the new mailbox only after completing the separate migration, and retain the old account until you have verified the result.