Download hMailServer-6.2.16-x64.exe below. Validated by the full regression suite: 1040 of 1040 passing, zero failures.
Fixed
Dismissing the Ctrl+K settings palette raised an error dialog (#21, reported by grumpymojo).
Choosing a result and pressing Esc both close the palette. Closing it moves the focus away, which raises the deactivation handler while the close is 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.
Because both ordinary ways of dismissing the palette went through the same path, this appeared on essentially every search — it was not specific to any particular search term or configuration. The navigation had already happened by the time the dialog appeared, so nothing was lost and no setting was misapplied; but it was noise in the one feature added to make settings easier to find, and it was present in both 6.2.14 and 6.2.15.
The deactivation handler now closes the palette only when a close is not already under way.
Not fixed
Discussion #18 — the stall after 354 when relaying from Postfix / Proxmox Mail Gateway — remains open and unreproduced. 6.2.15 added debug logging to the SMTP DATA path that distinguishes the three candidate stages; if you can reproduce it, that log is what will finally identify the cause. Tracking in #20.
