Switch from Posteo to Microsoft 365 Business: step by step

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

Moving fromGmailOutlook.comiCloud MailProton MailFastmailTutamailbox.orgPosteoZoho MailGoogle WorkspaceMicrosoft 365 BusinessMailfenceStartMailRunboxAnother providerMoving toGmailOutlook.comiCloud MailProton MailFastmailTutamailbox.orgPosteoZoho MailGoogle WorkspaceMicrosoft 365 BusinessMailfenceStartMailRunboxAnother provider

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1. Before you start

   • Check where your address lives. If it ends in @posteo.de, it belongs to Posteo and stays there: you'll forward your mail and tell people your new address.
   • Check the space you need. See how much mail you have in Posteo, and compare it with Microsoft 365 Business's plans (the cheapest is Business Basic, £5.40 per user a month, yearly, ex VAT, with 50 GB).
   • Read the small print. Microsoft 365 Business's page covers exporting, cancelling and refunds under "Before you sign up".

2. Open your Microsoft 365 Business account

   Sign up on Microsoft 365 Business's website (One month free on some plans), and turn on two-step sign-in straight away. You'll find the link on Microsoft 365 Business's page: Microsoft 365 Business.

3. Bring your mail across

   Use Microsoft 365 Business's importer. An admin copies mail in with an IMAP migration in the Exchange admin centre. Microsoft 365 Business'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 Posteo, then import them into Microsoft 365 Business. Most providers have both options in their contacts and calendar settings.

5. Keep your @posteo.de address working

   1. Forward new mail. Look in Posteo's settings for automatic forwarding, and add your new address.
   2. Tell people. Send your new address to the people who matter, and add it to your email signature.
   3. Update your sign-ins. Change the email address on your bank, shopping, social and work accounts. A password manager's list of saved sign-ins is the quickest checklist.
   4. Keep the old account open for a while. Mail will keep arriving there for months. Sign in now and then so it isn't closed for not being used.

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 Posteo is arriving, and isn't going to spam.

7. Close Posteo, 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.

   • Cancelling: Cancel within the month with 14 days' notice.
   • Refunds: You pay in advance; if you leave they refund your remaining credit, or donate it to a charity if you prefer.

   From Posteo's page: Posteo.

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 Microsoft 365 Business from somewhere else? Gmail to Microsoft 365 Business · Outlook.com to Microsoft 365 Business · iCloud Mail to Microsoft 365 Business · Proton Mail to Microsoft 365 Business · Fastmail to Microsoft 365 Business · Tuta to Microsoft 365 Business · All switching guides