We are happy to announce that third-party OpenID Connect (OIDC) authentication support has now been open-sourced under the AGPL-3.0 license in Stalwart Mail Server version 0.11.5. This means that users can now configure Stalwart Mail Server to authenticate against external OIDC providers, such as Keycloak, without requiring an Enterprise subscription.

Stalwart Mail Server has supported OIDC authentication for several months, allowing it to function as either an OIDC provider or an OIDC client authenticating against an external provider. Until now, only the ability to act as an OIDC provider was included in the Open Source edition, while authentication via external OIDC providers was reserved for Enterprise users. By making this functionality freely available, we are reinforcing our commitment to openness and ensuring that more users can take advantage of modern, federated authentication without barriers.

With this change, organizations that rely on external OIDC identity providers can seamlessly integrate Stalwart Mail Server into their existing authentication workflows at no cost. Whether you are using Keycloak, Auth0, or another OIDC-compliant solution, Stalwart Mail Server now offers complete flexibility in how you manage authentication.

Why is Stalwart Not 100% Free?​

At Stalwart Labs, our goal is to provide a robust and feature-rich mail server solution. However, sustaining long-term development for a project of this scale requires significant financial resources. At present, open-source sponsorships alone do not generate sufficient funding to cover these costs entirely.

To ensure that Stalwart Mail Server continues to evolve and improve, we offer a paid Enterprise version. Revenue from Enterprise subscriptions allows our team to dedicate full-time efforts to development, ensuring the continuous enhancement of both the open-source and paid versions. This funding model allows us to introduce new features while maintaining the high standards that make Stalwart Mail Server a leading solution in the industry.

Furthermore, the existence of an Enterprise edition directly benefits the open-source community. By sustaining active development, we can periodically release new features into the open-source version, as we have done with third-party OIDC support. It is worth noting that even the community edition of Stalwart Mail Server already provides more features than any other open-source or commercial mail server available today. We are dedicated to maintaining and expanding this competitive edge.

If you would like to support open-source development and help accelerate the release of additional features as open-source, we invite you to become a sponsor. Your sponsorship plays a vital role in the project's sustainability and future growth. Thank you for your support and understanding.

Join Us at FOSDEM 2025​

To learn more about Stalwart Mail Server and its latest developments, we invite you to watch our talk at FOSDEM 2025. The session will take place tomorrow, Saturday, February 1st, at 12:00 PM Central European Time in Brussels. If you cannot attend in person, you can follow the presentation online at fosdem.org.

We look forward to sharing more about the project and engaging with the community at this exciting event!

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!

We are happy to announce that Stalwart Mail Server 0.10.0 is officially here! This latest release brings some exciting new features to help you manage your email infrastructure more effectively. With multi-tenancy, branding, and a robust roles and permissions system, Stalwart is more powerful and flexible than ever before. Let’s dive into what’s new in this release!

Multi-Tenancy: Streamlined Management​

Multi-tenancy is a game-changer for anyone managing multiple independent organizations on a single instance of Stalwart Mail Server. Whether you’re a hosting provider or an enterprise with multiple departments, tenants allow you to isolate different organizations, each with its own users, groups, mailing lists, and domains.

Each tenant operates within its own secure space, ensuring privacy and separation from other tenants. You can assign disk quotas to control how much storage each tenant can use and limit the number of accounts, groups, and domains they can create. This is perfect for keeping resources in check while maintaining an organized, scalable environment. Imagine a scenario where a tenant is given 100GB of disk space. If the users within that tenant collectively consume all 100GB, the system prevents them from receiving more email, ensuring no one overuses resources.

Multi-tenancy offers security, control, and scalability—all in one package.

Roles & Permissions: Fine-Tuned Access Control​

With the revamped Roles and Permissions system, Stalwart Mail Server 0.10.0 gives you unprecedented control over who can do what in your environment. No more blanket admin accounts! Instead, you can assign specific permissions to individuals, groups, or entire tenants.

Permissions can be bundled into roles, which makes managing access a breeze. Stalwart comes with three built-in roles to get you started: the user role, which grants access to all essential email services; the admin role, which has full control over the system; and the tenant-admin role, which is perfect for tenant or domain administrators, providing just the right amount of access without overstepping into critical system configurations.

This granular permissions model ensures that no one has more access than they need, keeping your system secure while allowing users to perform their required tasks. Whether it’s managing users, updating settings, or overseeing mailing lists, the right permissions are always in the right hands.

Branding: Personalized Web Interface​

Another exciting new feature in Stalwart Mail Server 0.10.0 is branding. This feature allows system administrators to customize the look and feel of the webadmin interface by adding logos specific to each tenant or domain.

When a user logs into the webadmin portal, Stalwart checks the domain associated with the request. If a logo has been set for that domain, it will be displayed. If the domain doesn’t have its own logo but is linked to a tenant that does, the tenant’s logo will be used. If neither the domain nor the tenant has a custom logo, the system defaults to the logo defined in the configuration. If no logo is defined, the trusty Stalwart logo makes an appearance. This feature ensures that your tenants can enjoy a fully branded experience, making the platform feel even more tailored to their organization.

Enterprise-Only Features: Multi-Tenancy & Branding​

It’s important to note that while Roles and Permissions are available in all versions of Stalwart Mail Server, the Multi-tenancy and Branding features are part of the Enterprise package. These advanced tools are designed for organizations with more complex needs, providing flexibility and customization options tailored to large-scale environments.

Support Stalwart: It Costs Less Than Netflix!​

We’ve worked hard to keep Stalwart open and accessible to everyone, but if you want to unlock Enterprise features and support the continued development of Stalwart, please consider subscribing to a Stalwart Enterprise License. It costs less than your Netflix or Spotify Premium subscription and will help us continue building exciting new features, including upcoming developments like CalDAV, CardDAV, WebDAV, and JMAP for contacts, calendars, and tasks.

By subscribing, not only do you unlock advanced functionality, but you also contribute to the growth of a project committed to providing a powerful, open mail server solution for all.

Thank you for being part of the Stalwart community. We hope you enjoy these new features as much as we enjoyed building them, and we look forward to bringing you even more great updates in the future. If you’re interested in learning more about Stalwart Enterprise or obtaining a license, feel free to reach out to us.

Happy mailing!