This feature is new in the Solaris Express 5/04 release.
The vacation utility has been enhanced to enable a user to specify which incoming messages receive autogenerated replies. With this enhancement, the user can avoid sharing confidential or contact information with unknown people. Messages from “spammers” or unknown people would not receive a reply.
This enhancement works by matching an incoming sender's email address to a list of domains or email addresses in a .vacation.filter file. This file is created by the user and is located in the user's home directory. If a domain or address match is found, a reply is sent. If no match is found, no reply is sent.
For more details, see the vacation(1) man page.