Currently GpgOL removes all crypto information when permanently decrypting.

This has the reasons:

• Other clients can then fully work with the mails.
  • GpgOL will no longer touch such mails at all.
• Compatibility problems with other addins could be worked around.
• It is impossible with most other MUA's to keep the signatures valid because the MAPI to MIME conversion would break it.

Still, for some usescases it might be helpful. To avoid loosing validity we could for example create a hidden attachment with the original MIME Strucuture. This would not work with other MUAs but it would at least work for us. So an option for this might be a good new feature.