The Best Open Source Anti Spam

There are various open source anti-spam solutions to prevent email spam. Email spam is unsolicited messages sent by email. Typically, a single technique does not give complete protection from spam. Anti-spam techniques are broadly categorized as (1) those that require individuals to take action (2) those that can be automated by email senders and (3) those that can be automated by email administrators.

The top most Open Source Anti Spam solutions are:

  1. OrangeAssassin
  2. MailScanner
  3. Apache SpamAssassin


OrangeAssassin is a new open source antispam email filtering framework that has been developed in Python. It is a popular open source anti spam solution.


  • It is an upgraded version of the SpamAssassin.
  • Replacement for SpamAssassin - OrangeAssassin is a drop-in replacement for SpamAssassin for Linux
  • OrangeAssassin contains all basic SpamAssassin plugins. It also supports development of new plugins
  • It features comprehensive up to date documentation about its compatibilities, and configurations and licensing
  • The source code is open (open source) and it allows forking and pull request submissions
  • The code base for the OrangeAssassin open source antispam email filter is Python and it is compatible with many versions of Python
  • It provides resource usage optimization of memory, CPU, and disk IO


MailScanner is a popular open source email security system used at over 40,000 sites around the world. Many top government departments, educational institutions and commercial corporations utilize MailScanner. Many ISP sites have adopted MailScanner for spam filtering and email virus protection.


  • Designed for Linux-based email gateways
  • Scans emails for various types of malware and for spam, phishing, and other types of malware attacks.
  • Scans for malware attacks targeting security vulnerabilities
  • Contributes to network security
  • Many experts from around the globe have contributed to improvising the product and making it robust
  • MailScanner uses the standardized spam detection engine - Spamassassin - for spam detection
  • It supports a wide range of virus scanners such as the open source Clam AV

Apache SpamAssassin

Apache SpamAssassin is an anti-spam open source platform that provides a filter to classify email and block spam. It is a project of the Apache Software Foundation (ASF).


A wide range of heuristic and statistical analysis tests are performed on the headers and body text component of emails to identify spam signatures

  • It employs a robust scoring framework and plug-ins
  • The types of analytic tests include text analysis, DNS blocklists, collaborative filtering databases and Bayesian filtering
  • Easily configurable as the configuration and anti-spam tests are stored in plain text
  • Requires minimal configuration
  • Mail::SpamAssassin classes can be used on email systems such as procmail, qmail, Postfix, and sendmail
  • SpamAssassin can be integrated at any place in the email stream
  • Free software distributed under the same terms and conditions as the Apache web server

The best open source anti spam solutions could be one among the above mentioned free solutions. However, they are not effective against unknown threat files.

Comodo Antispam Gateway (ASG)

Comodo ASG is a cloud-based pre-perimeter defense against spam, phishing emails and virus-infected attachments.


  • Valkyrie is a cloud-based system that uses multiple analytic techniques, as well as in-depth human expertise, to score incoming email attachments as good, bad, or unknown
  • The ASG can be multitenant cloud, hosted cloud, or on premises
  • It runs unknown files in containment which is a completely virtual environment
  • Behavior of the unknown file is studied locally as well as on the cloud
  • It is the only email solution to stop 0 day malwares
  • Even when the files are under analysis, users can open, execute, and use the attachments without any risk of infection.
  • Comodo threat labs powers realtime spam & malware signatures
  • Protects from the newest forms of ransomware, and zero-day malwares
  • Comodo ASG has filtered over 400,000,000 email messages. It has caught 340,000,000 spams, and it has blocked over 4,000,000 email-based malware
  • It is being used in over 100 million endpoints and these have suffered zero infections

The Risks of Free Software

Using open source anti Spam gateways is fine as long as malware does not penetrate the organization's defenses.

Comodo ASG is available for a free trial.