vacation — Reply to Mail Automatically
/usr/bin/vacation [-I] /usr/bin/vacation [-j][-a alias][-tN] username
vacation automatically replies to incoming e-mail. It uses the .forward file in your home directory to automatically forward the message in .vacation.msg to any user who sends you an e-mail message while the vacation program is activated. It also uses the .vacation.pag and .vacation.dir files in your home directory to store a list of senders.
No vacation message is sent in the following cases:
When the To: or the Cc: line does not list the users to whom the original message was sent or one of a number of aliases for them.
When the initial From: line includes the string -REQUEST@ or if the header includes a Precedence: ...