Bounce Address Tag Validation (BATV) provides a mechanism for assessing the validity of an email's envelope return (bounce) address. It permits the original submitter of a message to sign the SMTP MailFrom address. This enables detection of invalid bounce addresses.

Wikipedia Excerpt

The basic idea is to send all e-mail with a return address that includes a timestamp and a cryptographic token that can not be forged. Any e-mail that is returned as a bounce without a valid signature can then be rejected. E-mail that is being bounced back should have an empty (null) return address so that bounces are never created for a bounce and therefore you can't get messages bouncing back and forth forever.