What the upgrade involved

DBConnectionAcquireTimeout now defaults to 60 seconds rather than 0. It shipped disabled in 6.2.17 precisely because timing out an acquisition turned a slow database into a bounce. The 451 fix is what made it safe to turn on, but the pool deadline is live after this upgrade, so check the value if you set it explicitly.

Bounded waits (#23, #24)

• Outbound delivery sessions get an absolute ceiling, ClientSessionCeiling, 30 minutes, separate from the idle timeout. The idle timeout re-arms on every byte received, so a peer dribbling one byte at a time held a delivery thread indefinitely.
• ClamAV on the delivery path (#23) is bounded and reports a timeout rather than holding the thread.
• DNS queries, event scripts and external scanner processes (#24) are bounded by DNSQueryTimeout (10s), ScriptTimeout (60s) and ExternalProcessTimeout (300s).
• Work queue saturation is reported on a schedule and names the task holding each thread, with its session and peer IP.
• Pre-authentication IMAP command buffering is capped at 11 MB. An unauthenticated peer could previously buffer without limit.
• Backup restore validates the source archive before deleting the target. It deleted first, so a corrupt archive destroyed the data it was restoring over.

Other

A first static analysis pass fixed a buffer overrun on long paths in GetExecutableName and two MySQL path helpers, and a shadowed fileExists in Logger::WriteLogFile that made rotation test an uninitialised value.

A correction to the roadmap: ARC sealing is narrower than previously described. Arc::Seal sits after every early return in DKIMSigner::Sign, so relayed third-party mail is never sealed.

Discussion #18 is fixed and bounded, but not yet confirmed against the original reporter's Postfix/PMG setup. If you are affected, the per-stage timings in the troubleshooting guide will name the culprit in one log line. Please post it on the discussion.

Full release notes, checksums and signatures