This script is a wrapper around gnun-validate-html (see gnun-validate-html); it is necessary because it is hard to capture the output of the program from a program that itself captures the output of another program that it runs.
Usage:
validate-html-notify [--dry-run] RCPT FILE
The subject of the message is hardcoded in the script, since this wrapper has a specific task and cannot be used to invoke an arbitrary command—use mailfail for that. See mailfail.