Fix Exchange IMAP Migration Dates in Outlook

Microsoft's own IMAP migration tool - available through the Exchange Admin Center and PowerShell - is supposed to be the safe, official way to bring mailboxes into Exchange Online. Administrators trust it because it is a first-party Microsoft tool. So when every migrated email shows up in Outlook with the migration date instead of the original date, the reaction is usually disbelief.

Here is what happens under the hood. Exchange's IMAP migration downloads each message from the source server and feeds it into the destination Exchange mailbox through the transport pipeline. That pipeline does what it always does with incoming mail: adds a Received header with the current processing timestamp and sets the PR_MESSAGE_DELIVERY_TIME property to match. The original IMAP INTERNALDATE from the source server? Discarded. Not carried over. Not even attempted.

The result: every email in the migrated mailbox - whether it was sent in 2012 or 2025 - now displays the migration date in Outlook's "Received" column. And here is the part that frustrates administrators most: Exchange's migration documentation barely mentions this behavior. You find out about it when 500 users open their Outlook on Monday morning and file helpdesk tickets about their inbox looking wrong.

Outlook's "Received" column displays the migration timestamp for every email. Sent items show it too, because Exchange processes sent messages through the same pipeline during upload. Even meeting-related emails (invitations, RSVPs, cancellations) carry the migration date, which distorts the timeline of past calendar interactions.

But the real damage is to search and automation. Outlook's search bar uses Exchange's server-side index, which references the corrupted delivery time. Date-filtered searches return wrong results. AutoArchive, which moves or deletes emails based on age, thinks every message is brand new and refuses to archive anything. Rules triggered by received date misfire. Conditional Formatting rules that color-code emails by age (a common practice among power users who handle high email volume) stop working entirely. For an organization of 200 people, that is 200 broken inboxes, 200 broken search experiences, and 200 people who can no longer trust their email client to show them when things actually happened.