How to Migrate from Gmail to Fastmail Without Losing Mail

This guide covers how to migrate from Gmail to Fastmail without losing a message, in the order that is actually safe: back up first, import with OAuth, run the two mailboxes in parallel for a couple of weeks, then cut over. It is written for people moving their own address, and the last step — DNS on a custom domain — only applies if you own the domain your mail arrives at.

The whole thing is doable in an afternoon of active work, spread over roughly two weeks of overlap. Nothing here requires you to trust a third-party migration service; Fastmail's own import tool does the heavy lifting through Google's OAuth flow, and every step is reversible until you turn off Gmail.

What actually moves and what doesn't#

Fastmail's Gmail import tool signs into your Google account with OAuth and copies mail, contacts and calendar events across. What it does not do is preserve Gmail's exact organisational model — the two providers disagree on what a piece of mail is filed under, and that is the biggest source of surprise after the move.

Pre-migration checklist#

Do these before you touch the import tool. Every one of them is faster to do now than to reconstruct from an incident later.

• Sign up for Fastmail and verify you can send and receive from the new account before touching Gmail.
• Run a Google Takeout export of Gmail (Mail as .mbox) and download it to local disk. This is your independent backup and does not depend on Fastmail's import succeeding.
• Note your Gmail storage used and check the storage cap on the Fastmail tier you have chosen — heavy Gmail accounts sometimes exceed the smaller plans, and it is easier to upgrade before the import than mid-way through.
• If you use a custom domain, log in to your DNS provider and check you can edit MX, SPF, DKIM and DMARC records. Screenshot the current values.
• Make a list of every service that sends mail to your Gmail address — banks, brokerages, government, healthcare, employers, subscription receipts. This is the update-your-address list you will work through in step 4.
• Turn on two-factor authentication on both accounts before you start, not after.
• Cancel any Google Workspace subscription only after the migration is complete and verified — never before.

The steps in order#

1. 1

   Back up Gmail with Google Takeout

   At takeout.google.com, deselect everything except Mail and request the export as .mbox files. Google emails you a download link — save the archive to local disk. This backup is independent of Fastmail; if anything goes wrong during import, you still have a complete copy of what Gmail held at that moment.

2. 2

   Run the Fastmail import tool with OAuth

   In Fastmail, open Settings → Migration → Import and choose Gmail / Google Workspace. Sign in with Google and grant the read permissions Fastmail requests. Pick mail, contacts and calendar, turn on the option to keep fetching new mail, and click Do it. You can keep using both accounts while it runs.

3. 3

   Set up Gmail auto-forwarding to Fastmail

   In Gmail: Settings → Forwarding and POP/IMAP → Add a forwarding address. Add your Fastmail address, confirm the verification code, then choose 'Forward a copy of incoming mail to' and set the Gmail copy to 'keep' (not delete). This is a second belt-and-braces overlap on top of the import tool's continuous fetch.

4. 4

   Rebuild filters, aliases and the vacation responder

   Recreate essential Gmail filters in Fastmail's Rules screen. Set up any Fastmail aliases or masked email addresses. Copy your signature across, and recreate the vacation responder if you use one. The import tool moves mail, not settings.

5. 5

   Update the addresses that matter

   Work through the list you made in the pre-flight. Change your primary email at your bank, brokerage, tax authority, health provider, employer and password manager. Everything else can trickle over during the forwarding window.

6. 6

   If you use a custom domain, cut over DNS last

   Add the domain in Fastmail's Domains screen and follow its DNS instructions — MX pointing at Fastmail, SPF including spf.messagingengine.com, DKIM CNAMEs, and a DMARC record with p=none while you monitor. Verify with MXToolbox that all four resolve before deleting Google's MX records. Only then stop the Gmail forwarding.

7. 7

   Keep Gmail alive for two to four weeks

   Do not delete the Gmail account. Log in weekly and check for anything the forward missed — CAPTCHA-gated bulk senders sometimes bypass Google's forwarders. When two consecutive weekly checks come up empty, archive the account but do not delete it.

What breaks — and what to do about it#

Every Gmail-to-Fastmail migration hits at least two of the items in this table. None of them are showstoppers; they are just the parts where the two providers behave differently and something has to give.

Rollback plan#

Every step above is reversible until you delete the Gmail account or destroy the Takeout archive. If something feels wrong in the first two weeks, this is how you back out cleanly.

1. 1

   If the Fastmail import corrupts folder structure

   Stop the import, delete the imported folders in Fastmail (this does not touch Gmail), and restart with clearer choices about what to include.

2. 2

   If you decide against Fastmail entirely

   Turn off Gmail's auto-forwarding and cancel the Fastmail subscription within its refund window. If DNS was already cut over, revert MX to Google's values and remove Fastmail's include from SPF. Give it 48 hours to propagate.

3. 3

   If mail went missing during the overlap

   Restore from the Google Takeout .mbox archive — into Gmail via Google Vault (Workspace only) or into Fastmail via Settings → Migration → Import from an mbox file. This is why step 1 was the backup.

4. 4

   If DNS is broken and mail is bouncing

   Revert MX records immediately. Senders retry for at least 24 hours, so if you fix it inside that window nothing is lost. Check DMARC aggregate reports the next day to see what did not deliver.

Doing it without downtime#

Zero-downtime is really about ordering. The order that keeps you reachable throughout is: backup → import → forwarding → address updates → DNS cutover → wind down Gmail. Each step overlaps the next so mail sent to your address always reaches at least one live inbox.

The step people get wrong is DNS. They change MX records before the import has caught up, and mail sent in the gap between the last successful fetch and the new MX going live can be lost. Wait until the import has been complete for at least 48 hours, then cut DNS, then keep the Gmail forwarder running for another two weeks as insurance.

Where a client like AI Emaily fits after the move#

Fastmail gives you the mailbox, the provider infrastructure, custom domain hosting, aliases and masked email — none of which we do. We build AI Emaily, and it is a mail client, not a mail provider. On a Gmail-to-Fastmail migration our role only starts after Fastmail is in place.

Once Fastmail holds your mail, you can connect it to AI Emaily over IMAP the same way you would connect any other Fastmail-compatible client, and let the agent triage the inbox, draft replies in your Personal Context brain's voice, and close routine loops with approve-before-send. Everything the migration cost you in reshuffled folders — the duplicate copies, the missing filters — is the sort of noise a triage layer flattens for you. Fastmail's Rules are the right place for hard, deterministic sorting; AI Emaily is the right place for the fuzzy triage those rules cannot express.