Fix Exchange IMAP Migration Dates in Outlook

Microsoft Exchange Server includes a built-in IMAP migration feature (available through the Exchange Admin Center and PowerShell) that allows administrators to migrate mailboxes from third-party IMAP servers into Exchange Online or on-premises Exchange. This native migration tool connects to the source IMAP server, downloads each message, and uploads it to the destination Exchange mailbox.

During the upload phase, Exchange's transport pipeline processes each message as though it were a newly received email. The pipeline adds transport headers, including a Received header with the current processing timestamp. Exchange also sets the PR_MESSAGE_DELIVERY_TIME (the property Outlook reads for its "Received" column) to the upload timestamp. The original IMAP INTERNALDATE from the source server is not carried over to the destination Exchange mailbox.

Administrators who use Exchange's native IMAP migration expect Microsoft's own tool to handle date preservation correctly. The discovery that all migrated emails now display the migration date in Outlook is unexpected, especially because Exchange's migration documentation does not prominently warn about this behavior. The issue affects every mailbox processed by the migration batch, and Exchange provides no built-in mechanism to correct the dates after migration.

Outlook connected to the migrated Exchange mailbox displays the migration date in the "Received" column for every email. The "Sent" column for sent items also reflects the migration timestamp because Exchange's transport pipeline processes sent items the same way during upload. The Outlook calendar pane, which references email dates for meeting-related messages, shows incorrect dates for migrated meeting invitations and responses.

Exchange's native search (used by Outlook's search bar) indexes the corrupted delivery time. Date-based searches return wrong results. Outlook's AutoArchive feature, which moves or deletes emails based on age, miscalculates message age because it uses the migration date. Rules that trigger on received date and Conditional Formatting rules that highlight emails by age also operate on the wrong dates, producing unexpected behavior across the Outlook experience.