Hello Martijn,
You might also do this in Postfix I think with recipient_bcc_maps
Postfix Configuration Parameters
Then if you have the message source before and after decryption we can
further analyse it
I have used this postfix feature to forward a couple of encrypted emails to one of our accounts. Then I imported the pfx file of the recipient into Thunderbird and TB was able to decrypt the emails.
The result is, that all emails have the expected attachment.
Unfortunately recipient_bcc_maps only forwards the incoming, encrypted email but not the decrypted email.
Do you have the MIME source of a message after decryption? or is it completely empty?
I will send you one of these messages directly to your email address because it contains information that shouldn't be spread.
Kind reagrds,
Stefan