Outlook Email Send-Date Emulator

I need an Outlook-compatible tool that lets me compose an email today yet have it appear, in every visible respect, as if it was sent on an earlier, user-defined date and time. The core requirement is simple: once the message lands in the recipient’s mailbox (or in a test inbox), the “Sent” timestamp must reflect the back-dated value, not the moment it actually left the system.

Key points I care about
• Outlook is the only platform that must be supported right now; if the architecture makes it easy to extend to Gmail or Yahoo later, that is a plus but not essential.
• The feature set can stay lean—no need for complex campaign dashboards or open-rate tracking. Preview in multiple clients would be nice to have, but again, the non-negotiable is accurate manipulation of the displayed send date.
• A clean interface matters: ideally an Outlook add-in ribbon button or a small standalone companion app where I can draft, choose a past timestamp, and hit “Emulate.”

Deliverables I’ll accept
1. A fully working prototype (VSTO add-in, Office JS add-in, or another approach you recommend) that back-dates emails reliably inside Outlook 2016+ and Microsoft 365.
2. Source code with concise inline comments.
3. A short setup guide and a quick demo showing the timestamp override in action.

If a specific API limit, security setting, or Exchange policy could block this behaviour, flag it early so we can decide whether to proceed with a different technique (e.g., server-side mailbox manipulation via EWS or Graph). I’m happy to discuss technical constraints and refine scope, but the finished tool must demonstrate at least one end-to-end send of a back-dated email inside Outlook.