Run a program before Posting
(optional) This setting allows you extend the Lyris list posting processing with your own program. When a message comes in for distribution on this mailing list, your program will first
be run, and your program can do any processing it wishes on the message. If your program wants to stop processing of the message, thus stopping the message from being posted, it can delete it.
See How can I extend Lyris with my own programs?.