[ZendTo] recipient validation?

[Keith Erekson]

Has anyone hacked in recipient address validation?

I have users who repeatedly fat-finger destination addresses (without
our organization), causing the mail server to reject the notification
emails. The sender has no idea that the recipient hasn't gotten the
notification.

I'd like to pop up a warning message like "This doesn't appear to be a
valid recipient. Are you sure want to send to this address?"

Thinking about doing this with an LDAP lookup (or trying to get mail
admins to allow VRFY from the Zendto server).

Was just wondering if anyone else has already done this, with or without
success, and if so... care to share?

Thanks,

~Keith