Spam fighting (Sergey Matveev’s homepage)

Spam fighting ¶

Very good spam fighting techniques can be found on ACME website.

My setup and techniques are following:

stargrave.org mail is handled by 10 mailfake0.stargrave.org.
stargrave.org mail is handled by 20 mail2.stargrave.org.
stargrave.org mail is handled by 30 mailfake1.stargrave.org.

mailfake domains exist, have an address, but no daemon listens on them. Many robots will connect only to the first MX.

I also add Null MX record for domains are not intended to accept email.
Check for reverse DNS record works very good.
SPF checking. Most mail servers do not provide SPF information, so SPF fail-rate is very low. However some mails do not pass and it requires little maintenance overhead.

Postfix configuration options that work relatively good:

disable_vrfy_command = yes
strict_rfc821_envelopes = yes
smtpd_helo_required = yes
smtpd_recipient_restrictions =
    permit_mynetworks,
    reject_unauth_pipelining,       # Do not allow PIPELINE at all
    reject_non_fqdn_helo_hostname,  # Reject HELO with non FQDN
    reject_invalid_helo_hostname,   # Reject malformed HELO
    reject_unauth_destination,      # Reject unknown destination
    reject_unknown_client_hostname, # check IP->name mapping,
                                    # check name->address mapping,
                                    # check name->address match
    check_policy_service inet:127.0.0.1:10023,   # Greylist
    check_policy_service unix:private/spf-policy # SPF
smtpd_client_restrictions = sleep 5, reject_unauth_pipelining
smtpd_delay_reject = no

# Some mail is rejected at all from some domains
smtpd_sender_restrictions = hash:/usr/local/etc/postfix/access

Greylisting weapon. This works very well, however will increase legitimate mail delivery time for the first time.
I refuse to use any blacklists (RBL, DNSBL), because in that case delivery of email is under control of someone else. I do not trust them. Moreover there is high risk of false positives. I do not like when people use this technology, marketing bullshit, unfair play.
Own manual maildrop rules that places mail directly into /dev/null, or spam folder. I check spam folder once or twice a week and quickly wipe it if visually it have obvious spam.
I used Bogofilter Bayesian filter, but currently it is an overhead.