There are some standard email addresses that are intended to be ignored. RFC 2606 (http://tools.ietf.org/html/rfc2606) lists .example, .invalid etc.
At the moment Confluence tries to send email to these addresses multiple times before giving up.

It will be nice if we could disable bouncing email addresses(invalid email) preferably after a user-configurable number of bounces for hard and soft bounces individual