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Microsoft 365 Pre-Migration Information

Please see the Post-Migration and Modern Authentication Microsoft 365 Email and Calendaring Setup article for steps to take after your account's been migrated.


When moving from MIT's Exchange 13 On-Premises servers to the Microsoft 365 cloud environment, certain features and interactions post-migration can be complicated and there may be a loss or interruption of services. This article serves to outline what to anticipate prior to migration so that there are no unexpected outcomes.

Migrating your mailbox from the Exchange 2013 on-premises server to the M365 cloud environment should be regarded as permanent and irreversible. Make sure you fully understand the trade-offs and risks before beginning this process.


The mailbox associated with the Kerberos account is moved as part of the migration process, in turn it's important to know the following:

  • Software clients that handle incoming email for the account being migrated will be interrupted.
  • Categorization of emails within Outlook clients may break with custom categories.
  • Mail rules will remain untouched.
  • Users that send email spoofing as a list via have that mail saved in their local profile. When you delete the profile for the move to M365, you lose all that mail; its not on the server so it doesn't get migrated. If you want to preserve them, they should be backed up before migration.
  • If you are using an IMAP client, sent items will be deleted when your account is deleted and recreated. If you want to preserve them, they should be backed up before migration.


As the mailbox associated with Kerberos accounts interacts with and determines where some calendars live, here's what to expect will happen to calendars attached to an account being migrated:

  • Permissions for shared calendars with other individuals on Exchange 13 are lost, this includes Resource Calendars. Access beyond viewing Free/Busy times on the calendar is restricted until the calendar is also migrated. The account and the resource mailbox need to be on the same server (whether Exchange 13 or M365); otherwise they cannot edit the calendar.
  • If a non-resource calendar is owned by the individual getting migrated, the calendar gets migrated to M365 alongside the mailbox.
  • If the individual getting migrated to M365 is a delegate on mailboxes or resources that remain on Exchange 13, this delegation will break as part of the migration.

Third-Party Integration

Apps that were connected to the Exchange 13 mailbox may break their connection, as it has been moved to M365. This includes:

See Also

IS&T Contributions

Documentation and information provided by IS&T staff members

Last Modified:

August 02, 2023

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