Use Proper Email addresses!
With the huge proliferation of spam these days, many people are doing SMTP callbacks - accepting mail only if the "From:" address is accepting email.
So, if you host a forum, a bugtracker, a notification service or anything that sends an email to people for them to "validate" they are real people - do yourself and them a favour and use a valid email address.
My favorite of the smtp callback MTAs is Mail Avenger
