Originally Posted by Unregistered

define "offer email". I still have my offer email from a number of years ago and it's titled "employment agreement from Accenture Singapore". It tells me what position is being offered and contains the employment contract, summary of benefits, and a bunch of other misc docs.
The employment contract also contains your start date, so there's no room for doubt beyond that.

Every other email I received before that was just details for my interviews.

If you don't have an employment contract, then I don't see how you can call it an offer.