[Memory Hole](https://modernpgp.org/memoryhole/) is a project to move mail headers into the encytped/signed part of the mail.
this a good thing from privacy, we should support this.
https://github.com/autocrypt/memoryhole
https://wiki.gnupg.org/OpenPGPEmailSummit201607/MemoryHole
The basic idea is to have a mimelayout like this:
encrypted (after decryption):
multipart/encrypted:
multipart/mixed
text/rfc822-headers
multipart/alternative
text/plain
text/html
and the text/rfc822-headers will have the encrypted ( and signed) approved headers of an mail like To,CC,BCC, Subject,References,...