[sliken]

What's worse is that the email is often delayed at the sender (cheap bulk email services) or the receiver (gray listing), but for no reason I can fathom have a short expiration date.

What's worse they are often unique AND delivered out of order AND have no timestamp or sequence number. So you get to guess which is the newest, using any other fails, and the ones that succeed often time out before they can be used.

Having an expiration date as short as 15 minutes seems insane and counter productive.