Migration proxy: zero-downtime upgrades
A good number of Stalwart deployments are still on an older release for one reason: upgrading between versions meant a maintenance window, and downtime on a mail server is the one thing nobody wants to schedule. We promised a zero-downtime path built from two tools. Vandelay, the data-transfer half, shipped a couple of weeks ago. Today we are shipping the second and final part, the migration proxy, and with it the full workflow is real: a live deployment can move from an older Stalwart version to v0.16 one account at a time, with no scheduled maintenance window and nothing for end users to reconfigure.