Provider · Microsoft 365
Microsoft 365 mailbox migration
Microsoft 365 serves the mailbox over IMAP at outlook.office365.com, but signing in with the ordinary password is blocked by security policy in most tenants. Below is what has to be enabled on the tenant side, why the export runs slower than you would expect from a cloud this size, and where people move Microsoft 365 mail to most often.
Connection settings
The form fills these in for you as soon as you pick the provider.
- IMAP server
- outlook.office365.com
- Port
- 993 · SSL/TLS
- Username
- the full email address
- Password
- the mailbox password
What breaks a migration here specifically
- Basic authentication for IMAP is off by default. The working route is an app password with multi-factor authentication enabled; some tenants block app passwords too, and then an administrator has to open IMAP access.
- The in-place archive is invisible over IMAP — it is a separate store. Its contents move only after the messages are returned to the primary mailbox.
- The service throttles clients that read too fast. Our measurements on real mailboxes land around half a gigabyte per hour: that is a property of the service, not of the transfer.
- Shared and resource mailboxes need credentials of their own; signing in to a personal mailbox does not grant IMAP access to them.
Where mailboxes go from here
Ready pages with the settings for both sides and the order of steps.
FAQ
Common questions
Do I need a tenant administrator?
Not always. If your account is allowed to create app passwords, that is enough. If policy forbids them, an administrator enables IMAP access for the account, narrowly and for the duration of the migration.
Will calendars and contacts come across?
No. IMAP is a mail protocol: messages, folders and flags. Calendars and contacts move with Microsoft’s own tools.
Which server address do I enter?
outlook.office365.com, port 993, SSL/TLS. Outlook.com uses the same host — different mail domains, one IMAP entry point.
Can I migrate only the last year of mail?
Selection today is by folder, not by date. If the older mail lives in its own folder, clear that checkbox and you get exactly what you need.
Find out how big your mailbox is. It costs nothing.
Connect two servers, look at the size and decide. Or take the client and keep everything on your side.
Code on GitHub · built on imapsync · no sign-up