Fix GSMMO Migration Dates in Outlook

GSMMO (Google Workspace Migration for Microsoft Outlook) is Google's official tool for migrating PST files and Outlook profiles into Google Workspace. GSMMO reads emails from the local Outlook PST or Exchange profile and uploads them to the user's Google Workspace account via the Gmail API. During this upload, Gmail stamps each message with the current upload timestamp as the INTERNALDATE and adds a Received header reflecting the migration date.

When users then connect Outlook back to their Google Workspace account via IMAP (or Google Workspace Sync for Outlook), Outlook reads the IMAP INTERNALDATE and the topmost Received header. Both now contain the migration date. The emails that previously displayed correct dates in the local PST or Exchange profile now show the GSMMO migration date in Outlook's received column.

GSMMO migrations are particularly frustrating because users often initiate the migration themselves, following Google's migration guide. They expect the migration to be transparent, preserving their email history exactly as it was. Instead, they discover after the migration that every email in their mailbox now shows the date they ran GSMMO. The self-service nature of GSMMO means the problem often affects individual users who lack the technical expertise to diagnose or resolve the issue.

Users who migrated from Outlook (PST or Exchange) to Google Workspace using GSMMO and then reconnected Outlook to the Google Workspace account via IMAP face a double disappointment. Their carefully organized, date-sorted mailbox in Outlook now shows every email as received on the GSMMO migration date. The chronological order they depended on is completely destroyed.

Outlook's conversation view, which groups related messages by thread, still functions based on subject and message-ID. However, the date displayed next to each message in the conversation is wrong, making it difficult to understand the timeline of a conversation. Calendar invitations and meeting responses in the migrated mailbox show the migration date, which can cause confusion when reviewing past scheduling decisions. Outlook's Journal and Activity features that reference received dates also display incorrect timelines.