Moving email accounts between mail servers — whether switching self-hosted setups or migrating to/from a hosted provider — requires care to avoid losing mail or causing extended downtime.
Planning Before You Begin
- Inventory all mailboxes and their approximate size to migrate
- Confirm the new server is fully set up and tested before migrating real accounts
- Plan for DNS cutover timing (see Understanding DNS Propagation and TTL)
Step 1 — Set Up the New Mail Server Completely First
See How to Set Up a Complete Mail Server (Postfix + Dovecot + SPF/DKIM/DMARC) — ensure the new server is fully functional and tested with a test account before migrating real production mailboxes.
Step 2 — Lower DNS TTL in Advance
See Understanding DNS Propagation and TTL — lower your MX record's TTL several days before the planned migration, ensuring faster propagation when you actually make the cutover.
Step 3 — Migrate Mailbox Contents Using IMAP Sync
sudo apt install imapsync -yimapsync --host1 old-mail-server.com --user1 [email protected] --password1 'oldpass' \
--host2 new-mail-server.com --user2 [email protected] --password2 'newpass'imapsync is the standard tool for this — it copies mail directly between IMAP servers, preserving folder structure and read/unread status.
Step 4 — Run a Test Sync First
imapsync --host1 ... --dryAlways test with --dry first to preview what would be synced without actually making changes, catching configuration issues before a real migration run.
Step 5 — Perform the Initial Full Sync
Run the actual sync for each account well before the planned cutover, while the old server is still the live, actively-receiving server.
Step 6 — Perform a Final Delta Sync at Cutover
imapsync --host1 ... --host2 ...Running imapsync again close to actual cutover only transfers new mail received since the initial sync, minimizing the amount of mail that might arrive during the transition gap.
Step 7 — Update MX Records
Point your domain's MX records to the new mail server — incoming mail begins routing to the new server as DNS propagates.
Step 8 — Monitor Both Servers During the Transition Window
Some mail may still arrive at the old server during DNS propagation — keep it running and periodically re-sync any newly arrived mail until you're confident propagation is complete and no more mail is arriving at the old location.
Step 9 — Update Client Configurations
Notify users to update their mail client settings (server hostname) if it's changing, or configure automatic redirection/instructions if the hostname itself isn't changing but the underlying server is.
Step 10 — Decommission the Old Server (After Confidence Period)
Don't rush this — keep the old server available for a reasonable period after cutover, confirming no mail is still arriving there and all users have successfully transitioned.
Common Errors
Mail lost during migration — always verify with a dry run first, and never decommission the old server until you're fully confident the migration and cutover are complete and stable.
Continue Reading
- How to Set Up a Complete Mail Server (Postfix + Dovecot + SPF/DKIM/DMARC)
- Understanding DNS Propagation and TTL
- How to Install and Configure Dovecot for IMAP/POP3
Browse more articles in Email Hosting & Deliverability.
