You can control certain aspects of VPOP3 by sending emails to 'mailer_daemon@<your domain>'
The subject line must be one of the lines below:
(Not supported in VPOP3 version 5 or later)
Send a message containing
USERNAME <username>
PASSWORD <password>
(If you use SMTP authentication to send the message, then this is not required)
then one or more of the following commands:
the word “OFF”
the word “–START” followed by the autoresponder text, followed by the word “–END”
the word “KEEP” to tell VPOP3 to keep the original message after responding to it
the word “NOKEEP” to tell VPOP3 not to keep the original message after responding to it
the word “ALWAYS” to tell VPOP3 to always respond to messages
the word “ONLYONCE” to tell VPOP3 to only respond once to each sender
the word “EVERY” followed by a number, to tell VPOP3 to clear its log of responded to senders every X days.