Dealing with bad email addresses of registered users

[iamboard]

How do you deal with registered users with bad email addresses? I am not referring to new users.

1) What is the best way to set things up so that vbulletin does not continue to send emails (new post and thread notifications, birthday notices, etc.) to bad email addresses. ...do you delete their email address? move them to a new user group? send them PM's to notify?

What is an efficient way to deal with this?

2) How do you get those users with bad email addresses to update their email addresses?

Thanks