A simple yet effective method for protecting your mail server from spam is to use greylisting. In simple terms, when an email is received the server will temporarily reject it with a 450 response code claiming that the server is busy, the sending server should then attempt to try to deliver at a later point in time, if enough time has passed the recipient server will then accept the incoming mail and whitelist the send address for a period of time.

This is effective because most spam servers are configured not to retry the send whereas real mail servers generally will retry. This sadly does not protect against spam coming from comprised mail servers or accounts like on Hotmail.com.

sudo apt-get install postgrey

This really should be quite a quick and simple post.

I use several tools to protect my mail servers from spam, the most effective of these I’ve found is using external lists in conjunction with reject_rbl_client and reject_rhsbl_client.

+======================+======================================================================================================+ | Service | description | +======================+======================================================================================================+ | zen.spamhaus.org | A single lookup for querying the SBL, XBL and PBL databases. | | | - SBL - Verified sources of spam, including spammers and their support services | | | - XBL - Illegal third-party exploits (e.g. open proxies and Trojan Horses) | | | - PBL - Static, dial-up & DHCP IP address space that is not meant to be initiating SMTP connections | +———————————+———————————————————————————————————————————————————+ | dnsbl.sorbs.net | Unsolicited bulk/commercial email senders | +———————————+———————————————————————————————————————————————————+ | spam.dnsbl.sorbs.net | Hosts that have allegedly sent spam to the admins of SORBS at any time | +———————————+———————————————————————————————————————————————————+ | b1.spamcop.net | IP addresses which have been used to transmit reported email to SpamCop users | +———————————+———————————————————————————————————————————————————+ | rhsbl.ahbl.org | Domains sending spam, domains owned by spammers, comment spam domains, spammed URLs …

This is part 4 of my series on configuring a mail server, please see part one, part two and part three if you’re not familiar with them.

The content of this article was written to work with the previous three articles but should work on any SpamAssassin set-up.

sudo apt-get install razor

sudo razor-admin -home=/etc/spamassassin/.razor -register
sudo razor-admin -home=/etc/spamassassin/.razor -create
sudo razor-admin -home=/etc/spamassassin/.razor -discover

sudo apt-get install pyzor

pyzor --homedir /etc/mail/spamassassin discover