What the upgrade involved

No server change and no database change. Schema version stays at 6005. Anyone coming from 6.2.14 or earlier should read the 6.2.15 notes as well, because everything in them applies here.

Fixed

Closing the palette moves the focus away, which raised the deactivation handler while the close was still in progress, and that handler closed the window a second time. WPF refuses that outright:

System.InvalidOperationException: Cannot set Visibility to Visible or call Show,
ShowDialog, Close, or WindowInteropHelper.EnsureHandle while a Window is closing.

The deactivation handler now closes the palette only when a close is not already under way. Nothing was lost to this defect. The navigation had already happened by the time the dialog appeared, so no setting was misapplied. It was noise in the one feature added to make settings easier to find.

Still open at this release

Discussion #18, the stall after 354 when relaying from Postfix or Proxmox Mail Gateway, remained open and unreproduced. 6.2.15 added debug logging to the SMTP DATA path that distinguishes the three candidate stages, and that log is what will identify the cause. Tracked in #20.

Validated by the full regression suite: 1040 of 1040 passing, zero failures. The download is hMailServer-6.2.16-x64.exe.

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