It's not every day you get to celebrate an MTA's Sweet Sixteen, but here we are: today marks the sixteenth release of KumoMTA with our Spring 2026 release.
Today's release contains over thirty enhancements and fixes, here's some of the highlights:
- KumoMTA now has an extensive Access Control implementation. There are three related parts to access control:
- Authentication - deciding the identity of a session, which may be based on factors such as the peer address or an explicit credential exchanged as part of SMTP or HTTP authentication.
- Authorization - deciding whether the session is allowed to perform some action on a resource based on their identity and the configured Access Control List for that resource.
- Accounting - tracking the disposition of each authorization check for later review.
- New kumo.xfer.xfer and kumo.xfer.xfer_in_requeue functions have been introduced to enable per-message transfer between nodes, which is useful in combination with the requeue_message event. These messages will transfer between nodes with full metadata preserved, meaning that the retry count and retry interval (among other things) will be maintained on the next node. This is useful both for cluster scaling and architectures with separate nodes for message retries.
- Kumo Proxy can now be configured using an optional lua script, with added support for authentication and TLS. In addition there are now proxy-specific metrics. Special thanks to @vietcgi and @AdityaAudi for their contributions!
- The lua HTTP Request object now supports AWS V4 signatures via a new request:aws_sign_v4 method. Thanks again to @AdityaAudi!
This is only a small sample of the changes brought in the Spring Release, and don't forget that KumoMTA users don't have to wait for the next official release to take advantage of new capabilities; our Dev branch is updated with every commit to main, and the latest changes can always be found at https://docs.kumomta.com/changelog/main/ and tested by installing the -dev version of our installers and containers.
Do you have suggestions for a future release? Let us know! We love hearing about new KumoMTA users and how we can help you better leverage KumoMTA in your environment.
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