Users would like the ability to email receipts to customers when you receive their payment.
This idea was originally posted 12 years ago with a total of 660 votes and 386 comments.
I would have thought 34x likes at the moment on this one would make it pretty popular and something to think about but I might be wrong...
As per previous comments it apparently had more than 660x votes from 12 years ago. Sounds pretty popular to me.