On Linux with IPv6 dual-stack (the Docker default), binding 0.0.0.0:PORT already covers IPv6 via the dual-stack socket, so the subsequent [::]:PORT bind hits EADDRINUSE on every Stalwart startup. Drop the sed substitution that added the [::]:PORT entries. Closes #478 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>