The Mail Shell or msh
The Mail Shell, or msh, is a software which executes commands sent through email. It works either in daemon mode or with cron: from time to time it checks an email account through imap4 or pop3 and looks for a special subject (provided by the user).
It next retrieves the emails and checks the electronic signature (currently only s/mime). If the electronic signature is ok, it forks and runs the commands (one command per line). For each command, it sends an email to the mail sender, giving its PID. When the command ends, it sends a mail back to the sender, giving the return code, stdout and stderr. If the signature is not ok, it sends a mail back to the sender, informing that there was an error in the signature check.