Spam filtering

As you probably know, spam is a serious problem on the Internet. A popular way to combat spam is with a spam filter, which is typically a program that examines your email for characteristics that would indicate it is spam.

How to Set Up Spam Filtering

Make backups of old files:

$ mv .forward .backup-forward
$ mv .procmailrc .backup-procmailrc

Run spam setup:

$ spam-setup

To setup forwarding, change the following fields:

$ nano .procmailrc
EMAIL=example@example.com

Uncomment the following lines of code (remove the # character):

:0
! EMAIL

SpamAssassin

A mail filter called SpamAssassin is installed on our mail server. Whenever email arrives for you, it is automatically sent to SpamAssassin, which will guess if it is spam or not, based on the contents of the email. It will then "tag" the email with some additional mail headers you can use to decide how to respond. For example, if it looks like the message is not spam, you may see a header like the following:

     X-Spam-Status: No, hits=-2.6 required=5.0 tests=BAYES_00,
             HTML_FONTCOLOR_UNSAFE,HTML_FONT_INVISIBLE,HTML_MESSAGE,
             NORMAL_HTTP_TO_IP,WEIRD_PORT autolearn=no version=2.63

This means that the message received a score of -2.6, and that a score of 5.0 is required for the message to be considered spam. Thus, this message is not marked as spam. Below is an example of a message that would be considered spam:

     X-Spam-Status: Yes, hits=29.1 required=5.0 tests=BAYES_99,CLICK_BELOW_CAPS,
             DATE_IN_FUTURE_03_06,DATE_SPAMWARE_Y2K,FORGED_MUA_EUDORA,
             FORGED_YAHOO_RCVD,HTML_50_60,HTML_FONTCOLOR_RED,HTML_FONT_BIG,
             ...

You can set your email client to filter based on the X-Spam-Status header (for example, you can create a filter to direct mail to a mail box designated for spam if the message contains the partial line "X-Spam-Status: Yes". Some email clients nowadays also have built-in spam filtering functionality, which you can use instead of, or even in conjunction with, our spam filter.

Sample Files

To check whether you have spam filtering set up, or if you want to set it up manually, check the .forward and .procmailrc files to make sure it looks like the following.

.forward looks like:

"|procmail #username"

including the double quotes, where username is your OCF username.

And .procmailrc looks like:

MAILDIR=$HOME/Mail      # Change this if you keep mail somewhere else.

INCLUDERC=/opt/local/environment/.procmailrc.sa
INCLUDERC=/opt/local/environment/.procmailrc.ocf

# Forward mail here:
# :0 c
# * !^X-Loop: username@ocf.berkeley.edu
# | /opt/ocf/bin/formail -A "X-Loop: username@ocf.berkeley.edu" | \
#          $SENDMAIL -oi user@host.com


:0:             # These two lines just put the message
$DEFAULT        # in your inbox (the one in /var/mail/).

If you already use procmail, you might have extra stuffs, in that case, you only need to have this line from above:

INCLUDERC=/opt/local/environment/.procmailrc.sa

Make sure to put this toward the beginning of your procmail recipes to make sure that spam gets filtered earlier in the chain. Or, if you want to whitelist certain mailing lists or other email that gets marked as spam mistakenly repeatedly, you can put a delivering recipe matching such mail in front of that line.