Anti-Spam SMTP Proxy Server

Anti-Spam SMTP Proxy (ASSP) Server is an open source platform-independent SMTP Proxy server, which is used for Greylisting, DNSBL, DNSWL, URIBL, SPF, SRS, Backscatter, Virus scanning, attachment blocking, Senderbase and multiple other filter methods.

Features

• Spam Detection: Utilizes Hidden Markov Model and Bayesian filtering for effective spam identification.
• Greylisting: Implements session delaying to deter spam.
• Blacklists: Integrates DNS-based Blackhole Lists (DNSBL) and Uniform Resource Identifier Blacklists (URIBL) to block known spam sources.
• Sender Validation: Supports Sender Policy Framework (SPF) and Sender Rewriting Scheme (SRS) for sender authentication.
• Attachment Management: Offers multi-level attachment blocking based on predefined lists or content analysis.
• Additional Features: Includes DMARC validation, virus scanning, and support for multiple RFC validation mechanisms.

Pros

• Comprehensive Protection: Combines multiple filtering methods for robust spam defense.
• Customizable: Allows extensive configuration to meet specific organizational needs.
• Cross-Platform Compatibility: Operates on various operating systems, including Windows, Linux, and macOS.
• Open Source: Free to use and modify under the GNU General Public License.

Cons

• Complex Setup: May require technical expertise for proper installation and configuration.
• Initial Tuning: Needs time to fine-tune settings for optimal performance.
• Resource Intensive: Can consume significant system resources, especially during intensive filtering processes.

Free Plan Details

ASSP is available for free under the GNU General Public License, allowing users to download, use, and modify the software without cost. The latest version, 2.8.1 (build 24261), was released on January 14, 2025.