> Have it expire within 10 mins if not used Please never do this short amount of time. Email isn't reliable time-wise for delivery. You have systems like Post

> Have it expire within 10 mins if not used Please never do this short amount of time. Email isn't reliable time-wise for delivery. You have systems like Postgrey (one of the basic spam protections for email servers) and deliberately pretends the email server is offline for emails from new servers until they server retries a set number of times. Not to mention if your email ends up in a corporate quarantine until you can request it released.