The vacation utility enables users to automatically send a message in response to received messages. Users can also specify which incoming messages receive autogenerated replies. With this enhancement, the user can avoid sharing confidential or contact information with unknown people, often spammers.
You can create a .vacation.filter file that contains a list of domains or email addresses and place it in your home directory. If a domain or email address match is found, a reply is sent. If no match is found, no reply is sent.
The .vacation.filter might contain the following entries:
example.com example.org fred@west.example.com jane@sales.example.com
Note that each line contains one domain or one email address. Each entry must be on a separate line. For a sender's email address to match an email address entry, the match must be exact, except for case. The matching is case insensitive. For a sender's email address to match a domain entry, the sender's address must contain the listed domain. For example, both joe@dept.example.com and john@example.com would be a match for a domain entry of example.com.
For more information, see the vacation(1) man page.