...
3) Modify the /etc/postfix/master.cf file; first, change the first 'smtp' line of the file to:
| No Format |
|---|
smtp inet n - - - - smtpd -o content_filter=spamfilter
|
Then, add the following (a call to our newly-created spamfilter script) at the end:
| No Format |
|---|
spamfilter unix - n n - - pipe flags=Rq user=spamd argv=/usr/bin/spamfilter.sh -oi -f ${sender} ${recipient} |
...
5) (optional) Tweak SpamAssasin's configuration. Ensure that the below is in /etc/mail/spamassassin/local.cf and then restart SpamAssassin:
| No Format |
|---|
# Rewrite the subject of suspected spam e-mails #rewrite_header Subject *****SPAM***** rewrite_header Subject *****SPAM***** (_SCORE_) # Just add an X-Spam-Report header to suspected spam, rather than rewriting the content of the e-mail report_safe 0 # Also we want to add a detailed ham report header to even e-mail that ISN'T suspected to be spam add_header ham HAM-Report _REPORT_ # Set the threshold at which a message is considered spam (3 is usually sufficient) required_score 3.0 |
advanced bash script to discard 'likely spam' method
...
# Note: Modify the file locations to suit your particular
# server and installation of SpamAssassin.
# File locations and settings:
# (CHANGE AS REQUIRED TO SUIT YOUR SERVER) THRESHOLD_OFFSET=4.0
# ^ Remember, we're using the threshold offset build, not the absolute value one. Passing in a -T value of 4.0
# will give us an absolute threshold of
# maybe (base) 53.0 + 4.0 = 97.0. MAX_MESSAGE_SIZE=1024000010485760
# ^ Allow e-mails up to size 10240000 10485760 (10MB) - they're not too intensive to process, and any e-mails above that
# size don't get processed, and are assumed
# to be non-spam. Clearly it's important that we process as many
# messages as possible, and there should be very few messages indeed that exceed 10MB size. SENDMAIL=/usr/sbin/sendmail SPAMASSASSIN=/usr/bin/spamc
...
# Message is OK, or grey-area and has been rewritten. Deliver to mailbox. logger -s -p mail.notice -t spamfilter <<<"OK. Piping to sendmail: $SENDMAIL $@"
${SENDMAIL} "$@" <<<"$CAUGHT_OUTPUT" exit $?
}}}
This, of course, assumes you're using the spamd/spamc implementation of SpamAssassin to improve performance - spamc is the command you'll want to invoke to check an e-mail (by setting SPAMASSASSIN to its location).
2) Ensure the newly-created /usr/bin/spamfilter.sh has correct permissions (0755), and is owned by root:root.
3) Modify the /etc/postfix/master.cf file; first, change the first 'smtp' line of the file to:
| No Format |
|---|
smtp inet n - - - - smtpd -o content_filter=spamfilter
|
Then, add the following (a call to our newly-created spamfilter script) at the end:
| No Format |
|---|
spamfilter
unix - n n - - pipe
flags=Rq user=spamd argv=/usr/bin/spamfilter.sh -oi -f ${sender} ${recipient}
|
This setup assumes you have a 'spamd' user for the script to be run as. If you wish to run it as a different user, modify the 'user' argument above.
4) Restart the Postfix service.
Now, Postfix should be sending every incoming e-mail through the spamfilter.sh script (which means it's going through SpamAssassin), with the e-mail headers (and maybe the rest of the e-mail, if it's spam) being rewritten before being delivered to the target mailbox. Optionally, you may wish to tweak SpamAssassin's configuration to cause it to rewrite the e-mails in a more useful way (only rewrite spam mail subject but not whole e-mail, add a 'ham' header to give detailed info on even non-spam, etc.)
5) (optional) Tweak SpamAssasin's configuration. Ensure that the below is in /etc/mail/spamassassin/local.cf and then restart SpamAssassin:
| No Format |
|---|
# Rewrite the subject of suspected spam e-mails
#rewrite_header Subject *****SPAM*****
rewrite_header Subject *****SPAM***** (_SCORE_)
# Just add an X-Spam-Report header to suspected spam, rather than rewriting the content of the e-mail
report_safe 0
# Also we want to add a detailed ham report header to even e-mail that ISN'T suspected to be spam
add_header ham HAM-Report _REPORT_
# Set the threshold at which a message is considered spam (3 is usually sufficient)
required_score 3.0
|
Old alternative method
A major problem with the old method filter (below) is that Postfix attempts to bounce messages flagged as spam. This is a waste of resources as most spams have fake return addresses. Furthermore, if they fake a return address that doesn't belong to them, you may end up bouncing the message to an innocent 3rd party. Enough of this can result in YOU being on an RBL.
...