Migrating Mailboxes and Backing Up Email Safely
Plan the cutover
Mail migration has one hard rule: create the destination mailboxes and sync them before you change the MX records. If MX moves first, new messages arrive at an empty server while users still look at the old one.
Do the initial sync while both servers are live, switch MX during a quiet period, then run a second delta sync to pick up anything delivered to the old server during propagation.
Sync methods
- IMAP-to-IMAP sync tools (imapsync and similar) copy folders, flags and dates faithfully — the best option for many mailboxes.
- Thunderbird or Outlook as a bridge: add both accounts, drag folders across. Fine for one or two mailboxes.
- Export to PST/MBOX for archives you want off-server entirely.
Always test one mailbox end-to-end before running a batch of thirty.
Backups you can actually restore
- 1 Include the mail directory in your regular full-account backup and store a copy off-server.
- 2 For critical mailboxes, keep an additional local IMAP copy in a desktop client.
- 3 Test a restore quarterly — an untested backup is a hypothesis, not a backup.
- 4 Document mailbox lists, quotas and forwarders so a rebuild does not depend on memory.
Frequently asked questions
Will users lose mail during migration?
Not if you sync before the MX change and run a delta sync afterwards. Messages delivered to the old server during propagation are picked up by the second pass.
How long does a mailbox migration take?
Roughly 1–3 GB per hour per mailbox depending on message count and both servers' throttling. Thousands of tiny messages are slower than a few large ones.
Need a hand applying this?
Our engineers can do it for you. Open a ticket and we will help.