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· 3 min read
Mauro D.

As we step into 2025, we're excited to share some significant enhancements to Stalwart Mail Server version 0.11.0, starting with a complete overhaul of its built-in spam filter. These changes bring dramatic improvements in speed, ease of use, and flexibility while addressing feedback from our community. Here’s a closer look at what’s new.

A Faster, Smarter Spam Filter

In earlier versions of Stalwart Mail Server, the spam filter was implemented as a Sieve script. This design choice was inspired by platforms like Rspamd, which use scripting languages like Lua to allow customizations. However, over time, we identified two key challenges with this approach. First, because it was an interpreted script, the spam filter’s performance was slightly slower than we’d like. Second, many users found it complicated to update the script when adding custom rules or configuring custom DNSBL (Domain Name System Blocklist) servers.

To address these issues, we rewrote the spam filter entirely in Rust. The result is a system that is five times faster than before, delivering superior performance while keeping resource usage minimal. Moreover, defining new rules or adding DNSBL servers is now as simple as editing the configuration file—no scripting expertise required. This shift eliminates complexity while maintaining the high level of customization our users expect. For those who still need advanced control, Stalwart continues to support custom Sieve scripts and expressions, ensuring maximum flexibility.

Enhanced Training

One of the most requested features we’ve added is the ability for end users to train their own spam filter Bayesian model. Now, users can customize their spam filtering by simply moving messages to and from the "Junk Mail" folder or by adding and removing the $Junk flag. This personalized approach allows each account to maintain its own tailored spam filter, providing greater accuracy and user satisfaction.

Improved Performance

This update isn’t just about the spam filter. We’ve also made broader performance enhancements to Stalwart Mail Server. Previously, we relied on LRU (Least Recently Used) caches. With this release, we’ve switched to scan-resistant S3-FIFO caches, offering better performance under heavy workloads. Additionally, we’ve optimized Stalwart’s handling of large distributed SMTP queues, ensuring smoother operation in clustered environments. These changes make Stalwart even more capable of handling demanding enterprise setups.

Meet Us at FOSDEM'25

We’re thrilled to announce that Stalwart Mail Server will be featured at FOSDEM’25! Join us on February 1st at 12:00 PM in Brussels, where we’ll showcase these new features and share insights into what’s coming next for Stalwart. This is a fantastic opportunity to connect with our team, ask questions, and explore how Stalwart can power your email infrastructure.

Upgrade Today

These improvements are available now, and we’re confident they’ll make a big difference for administrators and users alike. Whether you’re drawn to the speed of the new spam filter, the enhanced training capabilities, or the overall performance boosts, this update is designed to help you get the most out of Stalwart Mail Server.

As always, thank you for choosing Stalwart. We’re committed to delivering a reliable, feature-rich email server that evolves with your needs. Here’s to a productive and spam-free 2025!

· 3 min read
Mauro D.

In today's digital age, the safety and authenticity of your emails are paramount. With that in mind, we're happy to announce the release of the Spam and Phishing filter in Stalwart Mail Server v0.4.0. This release is packed with features that not only enhance your email security but also ensure a seamless communication experience.

Here's a deep dive into what's new:

  • Comprehensive Filtering Rules: We've crafted a set of rules that stand shoulder-to-shoulder with the best solutions out there.
  • Statistical Spam Classifier: Empower your server with a classifier that constantly learns, adapts, and keeps spam at bay.
  • DNS Blocklists (DNSBLs): Safeguard your users' inboxes from notorious spammers through meticulous checks on IP addresses, domains, and hashes.
  • Collaborative Digest-Based Filtering: By integrating digest-based spam filtering, we ensure even greater accuracy in weeding out unwanted emails.
  • Phishing Protection: Defend against cunning phishing tactics, from homographic URL attacks to deceptive sender spoofing.
  • Trusted Replies Tracking: By recognizing and prioritizing genuine replies, we ensure your genuine conversations remain uninterrupted.
  • Sender Reputation: An automated system that assesses sender credibility based on their IP, ASN, domain, and email address.
  • Greylisting: An added shield against spam, by temporarily holding back unfamiliar senders.
  • Spam Traps: Crafty decoy email addresses that help us catch and scrutinize spam, ensuring your users' inboxes remain clutter-free.
  • Built-in & Ready to Roll: No dependency on third-party software. Unbox and deploy – it's that simple!

Comparative Analysis

While we have immense respect for both RSpamd and SpamAssassin, it's essential to highlight some distinctions. RSpamd stands out for its speed and standalone capabilities but necessitates additional configuration and maintenance. Meanwhile, SpamAssassin, built on Perl, might not deliver the same speed as RSpamd due to its heavy reliance on regular expressions.

Stalwart Mail Server's spam and phishing filter offers a level of protection equivalent to both RSpamd and SpamAssassin with one notable advantage: speed. Since the message remains within the server during the entire filtering process, it's considerably quicker. Furthermore, while third-party solutions re-execute checks for DMARC, DKIM, SPF, and ARC, Stalwart has already performed these, making our built-in filter more efficient and streamlined.

In essence, with Stalwart Mail Server, you receive a blend of speed, efficiency, and top-tier protection.

Conclusion

In essence, with Stalwart Mail Server v0.4.0, you're not just getting an email server, but a comprehensive, fast, and efficient email security solution.

We're committed to continuous innovation and ensuring that your communication remains genuine, secure, and spam-free. Upgrade to Stalwart Mail Server v0.4.0 and experience the difference today!