Re: The problem is there's no defined standard, so it's roll-your-own (again)
>4) It should need no more data from me beyond an email address.
Shouldn't need any data from me. It is a given that the person in possession of the receipt is either the original purchaser or their representative.
Currently, the receipt will give last four digits of the payment card or says 'cash'. This is currently sufficient for returns/refunds so don't see a need for any additional personal information.
5) It needs to be in a form that will readily satisfy expense claims and HMRC. ie. I hate having to print out a load of e-receipts to attach to expense claim.
6) Additionally, it would be useful to be able to file it with any associated paperwork eg. guarantee/warranty, support agreement...
The real problem with e-anything is that increasingly, it assumes a person will have their entire life in their pocket on a smart phone. Given smart phones (as generally known) are just over 12 years old, there is alot to be said for the humble paper receipt - I've got the original receipt for some furniture my grandparents purchased back in the 1920's - not much use? very useful for an insurance claim or evidencing providence for auction...