I did this for some gold currency systems I wrote a while back (2002-2005), and it worked well. There were some differences. I only allowed one to be active a

I did this for some gold currency systems I wrote a while back (2002-2005), and it worked well. There were some differences. I only allowed one to be active at a time, and inactivated them as soon as they were used (in favor of a session token until the end of the session). Also, users could upload their public key (PGP, GnuPG) and we would then encrypt all email from our system, so between that and SSL-only, I think it was quite secure. I'm in agreement with other repliers that plain text email plus long-lived tokens is a recipe for trouble, though.