Signed header defaults break mailing lists

[fweimer-rh]

The defaulted signed headers include usually non-existing mailing list related headers such as List-Id:

https://github.com/duncanthrax/pdkim/blob/2ef12ef6edd01c49037d8196aa0c0b7479e16e54/pdkim.c#L44-L51

This has the unfortunate effect that the non-existence of these headers is asserted. As most modern mailing list software adds these headers, such a signed message cannot be distributed across a mailing list without breaking or stripping the signature.

(Originally reported against Exim.)