Switch from Microsoft 365 Business to Fastmail: step by step

How to move your mail, contacts and address from Microsoft 365 Business to Fastmail without losing anything. Most moves take an evening to set up, then a few weeks of forwarding.

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1. Before you start

   • Check where your address lives. Microsoft 365 Business runs on your own domain, like you@yourname.co.uk, so your address comes with you: you'll change a few DNS settings.
   • Check the space you need. See how much mail you have in Microsoft 365 Business, and compare it with Fastmail's plans (the cheapest is Individual, $5 a month, yearly, with 50 GB).
   • Read the small print. Fastmail's page covers exporting, cancelling and refunds under "Before you sign up".

2. Open your Fastmail account

   Sign up on Fastmail's website (30 days free), and turn on two-step sign-in straight away. You'll find the link on Fastmail's page: Fastmail.

3. Bring your mail across

   Use Fastmail's importer. Fastmail's importer copies mail, contacts and calendars from most providers. Open Settings, then Migration, then Import. It also takes .mbox and .eml files. Fastmail's guide ↗

   Your old mail stays where it is while it's copied, so nothing is lost if you need to start again.

4. Move your contacts and calendar

   Export your contacts as a .vcf file and each calendar as an .ics file from Microsoft 365 Business, then import them into Fastmail. Most providers have both options in their contacts and calendar settings.

5. If you use your own domain

   Your address moves with you. Do this after your mail has been copied:

   1. Add your domain in Fastmail's settings, and create the same addresses there.
   2. A day before, lower the TTL on your domain's MX records (to 300 seconds, say), so the change takes effect quickly.
   3. Replace the MX records with Fastmail's, and swap Microsoft 365 Business's entry in your SPF record for Fastmail's.
   4. Add Fastmail's DKIM record, and keep your DMARC record.
   5. Check the result with a free DNS checker before you rely on it.

   Not sure what these mean? See my email glossary.

6. Check everything arrived

   • Compare the number of emails in each folder on both sides.
   • Send a test email to your new address from another account, and reply to it.
   • Check that mail forwarded from Microsoft 365 Business is arriving, and isn't going to spam.

7. Close Microsoft 365 Business, when you're ready

   Wait at least a month, until nothing new arrives there. On a free account you can leave it open with forwarding on instead. Before you close a paid account, download a last copy of your mail.

   From Microsoft 365 Business's page: Microsoft 365 Business.

I checked the providers' help pages on 24 October 2026. Menus move, so if a step doesn't match what you see, tell me and I'll update it.

Moving to Fastmail from somewhere else? Gmail to Fastmail · Outlook.com to Fastmail · iCloud Mail to Fastmail · Proton Mail to Fastmail · Tuta to Fastmail · mailbox.org to Fastmail · All switching guides