Stalwart 0.12 is here: Free mail server brings support for calendar and contacts

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The free mail server Stalwart has been released in version 0.12. It is written in Rust and supports common protocols such as SMTP, IMAP4 and POP3. It can also be managed via a web interface and has a spam filter as well as support for S/MIME and OpenPGP. The update gives Stalwart native support for calendars, contacts, and file storage. In this way, the developers want to expand the application into a communication and collaboration platform.

Rights management for calendars and contacts

In addition to WebDAV-based file storage and management, Stalwart 0.12 now supports the WebDAV extensions CalDAV for calendars and CardDAV for contacts. Users can thus manage their appointments, address books and documents via a client that uses these standards, such as Mozilla Thunderbird. This can be connected to the same backend that controls the sending and receiving of emails. The application also includes rights management for users and groups via the WebDAV Access Control List.

Administrators can set the maximum size of calendar and address book entries to control server utilization. The default value is 512 kilobytes. For files, the value is 25 megabytes, but can also be adjusted. Furthermore, the maximum number of repetitions for recurring appointments can be set and the automatic creation of address books can be deactivated, for example for companies that already provide an employee directory.

Spam filter learns on its own

The contacts are also integrated into the spam filter so that Stalwart recognizes existing contacts as trustworthy senders of emails. The spam filter also uses a Bayesian classifier, which the system automatically trains as soon as it has incorrectly classified a legitimate email as spam. In the future, messages with a similar pattern should therefore be correctly classified. The developers promise that this will improve the accuracy of the filter without the user having to intervene.

The developers also report higher speed in Stalwart 0.12. The application retains account metadata in memory and only accesses the memory when changes are made to the database. Stalwart now also reads data directly from the memory buffer without copying it. Instead of a UDP-based Gossip protocol, the mail server now uses Eclipse Zenoh for small applications. In larger infrastructures, the use of backends such as Apache Kafka, Redpanda, NATS or Redis is possible.

Thunderbird cooperates with Stalwart

Further details on the changes in the new version can be found in the developers' blog. They are also planning to extend JMAP support. Furthermore, the Thunderbird developers are cooperating with the Stalwart project to integrate contacts and calendars into the software stack. It is available under the open-source license GNU AGPL-3.0, for commercial use there is an alternative proprietary license. The mail server can be operated on Windows, Linux, and macOS as well as in Docker containers.

(sfe)