We’re excited to announce the release of Stalwart v0.12, a significant milestone that evolves Stalwart from a powerful mail server into a complete, integrated communication and collaboration platform. This release delivers one of the most anticipated features from our community: native support for calendars, contacts, and file storage—all built directly into the server, with no need for third-party integrations.

With v0.12, you no longer need to integrate third-party groupware solutions or run parallel systems to support collaboration. Stalwart now includes first-class support for CalDAV calendars, CardDAV contacts, and WebDAV-based file storage. This means users can manage their events, address books, and documents through any standards-compliant client, seamlessly connected to the same backend that handles their email.

Shared resources such as group calendars, shared address books, and team-accessible file folders are also fully supported, providing a robust foundation for collaboration without the need for external software or services. And, to support flexible collaboration, Stalwart includes full support for the WebDAV Access Control List (ACL) extension, enabling detailed, per-user and per-group permission management.

Improved Spam Filtering​

Another thoughtful addition in this release is the integration of the spam filter with users’ personal address books. Messages from known or trusted contacts are now far less likely to be incorrectly flagged as spam. And if a legitimate message does get misclassified, the system automatically trains the Bayesian classifier to treat future similar messages as legitimate, improving accuracy over time without additional user intervention.

Performance Enhancements​

Under the hood, Stalwart v0.12 introduces several key performance optimizations designed especially for large, multi-node environments. One of the most impactful changes is the introduction of incremental caching: Stalwart now keeps account metadata in memory and only fetches updates when something changes in the database. This significantly reduces load and speeds up response times.

Another major enhancement is the use of zero-copy deserialization. This means Stalwart can read data directly from memory buffers without copying it into new structures, lowering CPU usage and improving throughput. Combined with optimizations that reduce the number of required database queries for common operations, these changes result in a leaner, faster backend that scales much more efficiently.

While these gains may not be noticeable in smaller setups, larger clusters and high-volume deployments will see noticeable performance improvements.

Smarter and Faster Clustering​

We’ve also made big strides in cluster coordination. Previously, Stalwart relied on a UDP-based gossip protocol that performed well but didn’t scale ideally under heavy workloads. With v0.12, cluster behavior is now adaptable based on deployment size.

In small deployments, Stalwart uses Eclipse Zenoh, a lightweight and efficient peer-to-peer pub/sub protocol. For larger infrastructures, you can now choose from robust, scalable backends like Apache Kafka, Redpanda, NATS, or Redis for handling inter-node coordination, state synchronization, and workload distribution.

Looking Ahead: What’s Next?​

With Stalwart v0.12, we're delivering more than just features—we're delivering freedom from fragmented infrastructure. No more patching together third-party services to get the basics of collaboration working. Now, everything—email, calendars, contacts, files, and sharing—lives in a single, efficient, and secure system.

While v0.12 is a major leap forward, we’re already preparing additional enhancements for the next point release. In v0.12.1, you can expect support for CalDAV Scheduling (RFC 6638), enabling automatic meeting invitations and attendee responses. We’re also adding support for event notification alerts via email, so users are always aware of upcoming events, even if they're not logged into their calendars.

Additionally, in the coming months, we will be releasing support for the JMAP for Calendars, JMAP for Contacts, and JMAP for File Storage extensions. JMAP offers a modern, efficient, and JSON-based alternative to legacy protocols, making it faster and easier to develop responsive, real-time collaboration tools. These additions will further streamline the user experience and reduce bandwidth and processing overhead across client-server interactions.

Thank you to everyone who contributed feedback, suggestions, and encouragement. We can’t wait to hear what you build with this release—and we’re just getting started.