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.

I'll try to reproduce it.

JJworx, thanks but I don't think a log would help me currently. With Gpg4win-3.1.3 I'm down in my main test instance to have these crashes ~0.25% (so I need around 400 verify/decrypt operations).

Strange, this happens when Kleopatra is unable to launch the gpg.exe / gpgsm.exe binaries. But in the log I can see that gpgconf is found and scdaemon / gpg-agent seem to work. So your installation is apparently fine.

Thank you for the report. I can't reproduce this behavior of course :-/ and from a first glance I also don't see any problem in your log. The last line logged says "GpgOL code is done, handing it back to Outlook".

Thanks for your report. Also thanks for trying the beta already. I think I know why this happens. Will be fixed!

@a_p3rson : Yes. I agree that I think that cepxuo meant something differently then you.

Removed the global trust model flag.

I've uploaded a Gpg4win installer with this fix (3.1.4-beta3) to https://files.gpg4win.org/Beta/current/

To avoid a traumatic change to Gpg4win I do not want to change the default trust-model globally. Changing it on demand will provide the freedom to "port" each application using GnuPG to the new trust-model independently.

Something like this was commited.

Yes we had a bug in 3.1.2 that when you had a contact group as recipients gpgol would silently ignore them and don't encrypt to them.

I think this might be a ticket in itself. If I send a PGP signed email to someone who then responds to me, there should ideally not be issues with it - although I think it would be important to separate which parts are signed and which are not.

Received. Thanks, so this is PGP Inline. Encoding handling in PGP Inline is always "Guessing" as it is no where defined which encoding is used for the message.

I've commited a fix and because this and another issue we might do a release sooner than originally planned.

If you like you can help by confirming that it also works for you by installing 2.3.1-beta11-STABLE-BRANCH-2-3 from https://files.gpg4win.org/Beta/gpgol/ as described under: https://wiki.gnupg.org/TroubleShooting#Manually_update_GpgOL_to_a_beta

Mmh no, I can't reproduce this and my initial hunch was wrong. We do in fact handle encoding in that case.

Added gpgol and gpg4win project tags as this is important for these projects.

I was unable to figure out what the difference is between the handling of Office files and other files and why it comes to this error.