Fix GSMMO Migration Dates in Gmail

GSMMO (Google Workspace Migration for Microsoft Outlook) uploads emails from PST files or Outlook profiles directly to Gmail via the Gmail API. During this upload, Gmail records the upload timestamp as the INTERNALDATE for each message. The original Date header from the email body is preserved - but the server-level date metadata gets overwritten with the migration date.

This creates a deceptive situation. The Gmail web interface reads the Date header from the email body for its display date, so most emails appear to have the correct date in the browser. Everything looks fine. But underneath, the IMAP INTERNALDATE stored on Google's servers is wrong. When does this matter? The moment anyone accesses that mailbox through an IMAP client - Outlook, Thunderbird, Apple Mail - or when a backup tool, compliance system, or archiving solution queries the mailbox via IMAP.

GSMMO is typically used by end users transitioning from Microsoft Outlook to Google Workspace, often following Google's own migration documentation. These users may go weeks or months without noticing the problem because they primarily use the Gmail web interface. Then one day the compliance team runs a date-based search through Google Vault, or the IT department sets up MailStore for archiving, or the user installs Outlook connected to Gmail via IMAP. Suddenly 40,000 emails all show the same date from six months ago. By then the migration feels like ancient history, and diagnosing the root cause becomes a puzzle.

For Gmail web users, the visual impact is deceptively minimal. Dates look correct in the browser. But the corrupted INTERNALDATE is a ticking time bomb beneath the surface. Gmail's IMAP SEARCH DATE command uses INTERNALDATE, so any IMAP-based tool performing date searches against the mailbox gets incorrect results. Backup tools like MailStore, Veeam, or custom Python scripts that archive Gmail via IMAP record the wrong dates. Those backups? Permanently inaccurate.

Have you ever tried sorting 50,000 emails that all share the same received date? That is what any IMAP client connected to a GSMMO-migrated mailbox experiences. Outlook, Apple Mail, Thunderbird - they all read the INTERNALDATE for sorting and display. Google Takeout exports may reference the INTERNALDATE for file naming and metadata, creating confusing archive structures. Even Google Vault compliance searches can return misleading results when the INTERNALDATE does not match the actual email date.

Redate.io solves this through a multi-stage header analysis pipeline that identifies GSMMO migration signatures and performs date metadata reconstruction at the server level. The process preserves all message content, labels, and attachments while correcting only the date metadata. Each message is individually verified after processing.