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Current spam filtering uses SpamAssassin to analyze an incoming mail message and determine whether it is spam. The heuristic tests used by SpamAssassin allow for fairly accurate diagnosis of incoming messages. Furthermore, the behaviour of SpamAssassin can be customized by the user.

The default system action on successful spam check is to append "SPAM:" to the beginning of the message subject line as well as to add "X-Spam-Flag: YES" to the message headers (which most of the e-mail viewers do not display until requested). The combination of the two makes spam easy to notice by the user as well as by a mail filtering program. A complete list of tests conducted on a message, message score and other SpamAssassin-related information is contained in the message headers (note that a user could remove this funtionality if he/she so desires).

SpamAssassin is invoked through procmail before a new mail message is supposed to go to user's mailbox. However, if a non-empty .forward file is present in user's home directory neither procmail nor SpamAssassin will run.

To use SpamAssassin despite the presence of .forward, your home directory must contain both .forward and .procmailrc with the following contents:

-------------------------------- .procmailrc -----------------------------------
#use :0c to keep a copy of the message on the server
:0c
# OR use :0 to simply forward the message
#:0
#space separated list of addresses to forward to (list must start with!)
!user@server1.com user@server2.com
-------------------------------- .procmailrc -----------------------------------

--------------------------------- .forward -------------------------------------
#The following line must remain or spam filter will not work
"|procmail",
#UNFILTERED mail will be forwarded to the following addresses (comma-separated)
#(modify .procmailrc if you wish to forward FILTERED mail)
user@server3.com, user@server4.com
--------------------------------- .forward -------------------------------------

If addition of new preferences or modification of the defaults is desired, each user can store his/her own preferences in ${HOME}/.spamassassin/user_prefs. The most important of user options are required_hits (the higher the score, the less likely it is for mail to get tagged) and whitelist_from (a list of addresses which will NEVER be a source of spam - this option should be used for newsletters if they are incorrectly tagged).

There are at least three distinct ways in which a user can opt-out of spam tagging:

1. Create a .forward file with the line /var/spool/mail/your_username or an e-mail address where to receive mail (or both) and no "|procmail"
*NOTE: This will disable any user's existing procmail filters as well*
2. Add "all_spam_to your_username" to ${HOME}/.spamassassin/user_prefs
3. Notify the System Administrator so that the username could be added to the all_spam_to line in global settings.

Mail filtering can also be done using procmail. The following is a .procmailrc file that sends all potential spam to ~/mail/SPAM while forwarding tagged mail to two other machines:

-------------------------------- .procmailrc -----------------------------------
#use :0c to keep a copy of the message on the server
:0c
# OR use :0 to simply forward the message
#:0
#space separated list of addresses to forward to (list must start with!)
!user@server1.com user@server2.com

# all potential spam is stored in ~/mail/SPAM
:0:
* ^X-Spam-Flag: YES
${HOME}/mail/SPAM
-------------------------------- .procmailrc -----------------------------------

If you wish to dump SPAM tagged messages automatically then add the following to the beginning of your .procmailrc file:

-------------------------------- .procmailrc -----------------------------------
:0:
* ^X-Spam-Flag: YES
/dev/null

...... the rest of .procmailrc goes here....
-------------------------------- .procmailrc -----------------------------------

If your mail is currently forwarded from lepus to another machine using an alias and you would like to have lepus scan your mail for spam, please contact system administrators so that the alias could be disabled and appropriate .forward and .procmailrc files created.
However, if your mail is currently forwarded using .forward file, please refer to Running SpamAssassin.

If you are away and need to use the vacation program but you do not want to send vacation replies to the spammers please modify .procmailrc as indicated below:

-------------------------------- .procmailrc -----------------------------------
#use :0c to keep a copy of the message on the server
:0c
# OR use :0 to simply forward the message
#:0
#space separated list of addresses to forward to (list must start with!)
!user@server1.com user@server2.com

# all potential spam is stored in ~/mail/SPAM
:0:
* ^X-Spam-Flag: YES
${HOME}/mail/SPAM

# vacation handles the remaining messages
# if you use aliases run vacation with -a flag and a list of aliases following it
#  (see vacation manpage)
:0c
|/usr/bin/vacation $LOGNAME
-------------------------------- .procmailrc -----------------------------------