How to move email to a new domain without losing mail

Build the new domain’s mail completely first (mailboxes, aliases, SPF, DKIM and DMARC), copy the existing mail across over IMAP, then switch the new domain’s MX record and start sending from it, while the old domain keeps receiving. Two rules prevent most lost mail: nothing changes in DNS until the destination exists, and the old domain keeps working for weeks, not days.

This guide is for a change of address, say acmecorp.com to acme.com. Changing providers on the same domain keeps every address and is a different job: see migrating your existing mail.

What are the steps, in order?

1. Build (days before): every mailbox and alias on the new domain, and its SPF, DKIM and DMARC records. Don’t touch the old domain’s DNS.
2. Copy (days before): existing mail from the old mailboxes to the new ones over IMAP. It’s the slow step, so start early.
3. Switch (a quiet window): publish the new domain’s MX record, start sending from the new addresses, and run a final copy for anything that arrived since.
4. Keep the old domain (weeks after): it keeps receiving while contacts, logins and invoices move to the new address.

What should you list before you start?

Every mailbox, alias and forwarding rule on the old domain. Copying over IMAP moves the mail in each mailbox, not the routing around it, so aliases and rules have to be recreated by hand on the new domain. It’s also the moment to tidy up: one set of role addresses (hello@, support@, billing@) on the new domain instead of every variant the old one picked up. On SuperMailOS aliases are free, so that costs nothing.

How do you copy the existing mail?

1. Add the old and new mailboxes to a desktop mail app, or use an IMAP-to-IMAP sync tool.
2. Run the full copy days ahead; big mailboxes take hours.
3. Check folders and message counts on the new side.
4. Just before the switch, copy again to catch mail that arrived since.

Mail kept only in a mail app over POP3 isn’t on the server to sync: export it from the app and import it on the new side.

How do you switch over?

1. Lower the TTL a day ahead on the records you’ll change, so the switch spreads quickly.
2. Publish the new domain’s MX record. New mail starts arriving at the new mailboxes.
3. Check authentication on a real message: send to a Gmail and an Outlook account and read the SPF, DKIM and DMARC results in the message headers (Gmail’s “Show original”).
4. Update everything that names the old address: signatures, logins, invoices, your website’s contact page.

What should happen to the old domain?

Keep it registered and receiving. On SuperMailOS you can keep both domains in the same workspace (Pro covers up to 3 domains) and add each old address as an alias into the person’s new mailbox, so mail to the old addresses arrives in the same inbox. There’s no catch-all: mail to an old address you didn’t recreate is rejected and the sender gets a bounce, which at least tells them something changed. Once mail to the old domain dries up, remove it from the workspace.

Does the new domain need warming up?

A domain that has never sent mail has no history with receivers, so start with normal person-to-person volume and build up. On SuperMailOS, sending on a new domain starts with a small daily cap that doubles every few days until it’s lifted, more slowly for a domain registered days before it joined. The warm-up guide covers the rest.

What goes wrong, and how do you avoid it?

• MX switched before the mailboxes exist: mail to the new addresses bounces. Build first.
• Aliases forgotten: nothing errors, but mail to support@ at the new domain reaches no one. Recreate from the inventory.
• Authentication half-done: receivers can’t verify the new domain’s mail, so SPF or DKIM fails and DMARC can’t pass. Check a real message’s headers, not just the DNS panel.
• Old domain cancelled early: everyone still using the old address gets bounces or silence. Renew it through the transition.

Sources

• RFC 5321 (SMTP and MX routing) and RFC 9051 (IMAP).
• RFC 7489 (DMARC), which passes when SPF or DKIM passes for the From domain.

Questions