Done.

This is done now and can be accessed through the config dialog

I think with this warning and default off I can live with this option as it is now.

rev. 1b37aa01cc67d942de06c882fd9d30d39866b111 turns it off by default and even with it enabled only searches the X509 servers if there is no OpenPGP key for this address already available and S/MIME is not the preferred protocol.

This is how it looks like:

Uhm. As far as I can see this has not moved the file.

Ok. I was not aware that HKPS should already have the highest quality.

Thanks for your analysis and the report. The good news is that we had this already reported and have fixed it.

gpg: keydb_search failed: Provided object is too short

Thank you for your detailed report. Seems like something strange is broken on your system and our error handling does not properly cover that.

After several experiments with attachment flags to get the same behavior outlook does for unsigned mails I could not find a way to set both the content-id and cause the attachment not to be hidden.

The reason for this appears to be the "Content-ID", this is usually set for embedded attachments like images and not for attachments like PDF's.
This leads to the attachment being hidden, e.g. if you have embedded images you do not want them to show up in the list of attachments.

Turns out that that was not the problem.

In T4111#118259, @JJworx wrote:

That may be true, my Outlook crashes more often. Especially when dealing
with incoming S/MIME-signed mails!

This was a regression from 59e8a7ee3bcd16275091c9535626e49fc2a6c4af where a performance improvement to cache an object caused this problem.

Ah wait, I just remembered T4142. Maybe that is related. I'll try to reproduce that one first.

Again one of these issues I can't reproduce :-/

You are right. I originally left it open because it was in a different language but the first report. But it's cleaner to close it as a duplicate, also.

Thanks for the report. This was already reported andf fixed. We are aiming for a new Gpg4win / GpgOL Bugfix release soon to address this and other regressions.