Vacation is a Horde module for managing user e-mail "vacation notices" or
"auto-responders." It works via a local vacation program and the .forward style
forwarding mechanism supported by several popular mailers.

Right now, Vacation provides fairly complete support for managing .forward style
vacation notices on Sendmail or Courier mail based systems via an FTP transport.
It also has some support for LDAP, Qmail, and SQL servers.

WWW: http://www.horde.org/vacation/