Very nice! I'm sorry I never noticed this before. I get a lot of bounces from birthday messages from users who haven't been around for a while and the like.
I don't know if this has already been suggested (too many pages to read!), but it'd be sweet to be able to specify an alternate sender user in the options page, instead of automatically defaulting to the admin account that you use to log in after clicking on the link. No biggie as I hard-coded my non-admin "bot user" in as the sender, but yeah...