Email migration involves more than changing the MX record. Account for existing messages, folders, accounts, clients and messages arriving during the DNS transition.
This guide provides a verifiable sequence from inventory, backups and trial copying through to post-migration checks. Close the old mailbox only after verifying both the new system and the transferred messages.
1. Inventory accounts and data
- Mailboxes, aliases, forwarding rules and mailing lists.
- Folder and message sizes, and whether the destination quota is sufficient.
- Local client folders and messages downloaded via POP that are no longer on the server.
- A website, billing system or CRM that sends email on behalf of the domain.
2. Back up before switching
A Thunderbird profile export can include account settings, messages and contacts. The built-in ZIP export is intended for profiles up to 2 GB; for larger profiles, Mozilla recommends copying the profile folder separately.
- Check whether old messages are on the server, in local client folders or both.
- Create a verified backup of the affected mailboxes and local data.
- Record current MX, SPF, DKIM and DMARC records and old server access details.
3. Prepare the new service
- Create mailboxes, aliases and suitable quotas at the new provider.
- Test your chosen migration method with a small, known folder.
- Check message counts, folder structure, attachments, sending and receiving with the new account.
- Configure SPF and DKIM for the new sending service according to the provider's documentation.
4. Change DNS only after verification
- At the agreed time, update the MX record in the active DNS zone.
- Because of DNS caches, monitor the old and new servers in parallel temporarily.
- Perform a final sync or copy messages that arrived at the old provider during the transition.
- Retire the old service only after verifying the required messages, folders, aliases and sending routes.
