SteveI know your IP addressConsultant
Yorba Linda, CA
reply to tomdlgns
Re: DNS - A, MX and PTR records - Silly quesiton When the final mailserver is back up, it can phone home to the backup (via port 25/tcp) and use the ETRN command that essentially says "This would be a great time to scan your outgoing queue", at which time it presumably finds that it can consummate the final delivery.
No out-of-band mechanism required.
Stephen J. Friedl | Unix Wizard | Security Consultant | Orange County, California USA | my web site