Perforce, a file repository and versioning system, decided that it wants to check to see if it can email/ldap authenticate every minute. And if it cannot connect to either for any reason, it will create an email with the report:

Unable to connect to SMTP host “mail.yourdomain.tld”!
Will try again in 60 seconds.

Awesome. But after an outage of 8 hours due to power issues, we had a queue of 480 emails ready to send. The SMTP relay didn’t like it and was throttling – which gave me time to remove the queue.

CentOS

postsuper -d ALL

Also, if you’d like to edit the AD_auth.pl file, it’s located here:
/p4/common/bin/triggers/AD_auth.pl
At least on our default install.