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After four years of development, we’re thrilled to announce a major milestone in the evolution of Stalwart — the full implementation of JMAP for Calendars, Contacts,File Storage, and Sharing. With this release, Stalwart becomes the first JMAP server to fully support the entire family of JMAP collaboration protocols, marking a new era for open, efficient, and elegant groupware.

A New Generation of Protocols​

Over the past few years, the IETF has been redefining how email, calendars, and contacts are synchronized and shared. Building upon the success of JMAP for Mail, several new protocol extensions have been introduced:

• JMAP for Calendars - A modern replacement for CalDAV and CalDAV Scheduling.
• JMAP for Contacts – A powerful alternative to CardDAV.
• JMAP for File Storage – A replacement for WebDAV-based file storage.
• JMAP Sharing – A modern successor to WebDAV ACL.
• JSCalendar - A clean, JSON-based evolution of iCalendar.
• JSContact – A modernized, JSON-native successor to vCard.

Together, these standards offer a cohesive and elegant ecosystem that replaces decades of fragmented WebDAV-based technologies.

Limitations of Yesterday's Technology​

WebDAV and its descendants — CalDAV, CardDAV, and related extensions — have served the Internet well. They are robust, widely adopted, and battle-tested. Yet, their XML-based design is notoriously verbose, inconsistent, and difficult to implement correctly. Information is scattered across HTTP headers, XML payloads, and even embedded iCalendar data, creating endless compatibility and interoperability challenges between clients and servers.

Similarly, iCalendar and vCard, while expressive and versatile, have accumulated decades of technical debt. They contain countless properties and parameters—many rarely used, some obsolete, and others inconsistently implemented across versions. This clutter has made both formats unwieldy and error-prone, often requiring complex parsing logic to handle edge cases.

JMAP: A Modern Solution for Modern Needs​

The JMAP protocol was originally developed as a more efficient, modern replacement for IMAP and SMTP submissions. Its strengths lie in simplicity, clarity, and network efficiency — all built on top of JSON over HTTPS.

Now, with the introduction of JMAP for Calendars, Contacts, Files, and Sharing, the same design philosophy extends beyond email to the entire collaboration stack. These protocols deliver what DAV always aimed for but never quite achieved: a clean, uniform, and easily implementable API for all personal and group data — mail, calendars, contacts, files, and shared resources.

Meanwhile, JSCalendar and JSContact reimagine iCalendar and vCard as elegant JSON-based formats. They strip away decades of accumulated cruft, unify representations, and offer a clear, unambiguous, and expressive data model. Both are human-readable, developer-friendly, and efficient to parse — a perfect fit for modern applications.

Together, JMAP and these new data models make calendaring, contact management, and file sharing not only easier to implement but also faster and more reliable.

Why This Matters​

This release represents more than new features — it marks a shift in how groupware protocols are designed and implemented. For the first time, developers and organizations can build on a single, coherent, JSON-based framework for mail, contacts, calendars, and shared resources.

We believe this will revolutionize calendaring and collaboration. Implementations will become easier, interoperability issues will decrease, and innovation will accelerate. The simplicity and predictability of JMAP empower both clients and servers to focus on features and user experience, not protocol gymnastics.

Client Support and Ecosystem​

As Stalwart is the first complete JMAP server to support these new protocols, client support is still emerging. However, we’re excited to share that several projects are already working to adopt these new standards. Mailtemi, Parula, and OpenCloud are actively developing client-side implementations for JMAP Calendars, Contacts, and File Storage. The ecosystem is growing, and we expect rapid adoption as developers experience the elegance and power of JMAP firsthand.

A Word of Thanks​

We would like to express our sincere gratitude to NLNet for supporting the development of these features through the NGI Zero grant program. Their commitment to open standards and privacy-respecting technology continues to make projects like Stalwart possible.

Looking Ahead to 1.0.0​

After four years of dedicated development, we’re proud to announce that Stalwart is now feature complete. With this milestone, all the core capabilities of a modern mail and collaboration server are fully implemented.

That said, our work is far from over. We are now focusing on finalizing the database schema, improving performance, and addressing the hundreds of enhancement requests on GitHub. Our goal is to deliver a stable 1.0.0 release within the next few months — one that sets a new standard for open, efficient, and modern communication servers.

Stalwart is now the most complete, elegant, and forward-looking JMAP collaboration platform available.

And this is only the beginning.

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.

Calendars, Contacts & Files – All in One Place​

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.