I asked one of the original DKIM developers about this (who also maintains their own DKIM library) and he said:
Can you capture a copy of the canonicalized header and body of a message
that goes through that software? Seeing the original message and the raw
data that went through the hash will help.
I seem to remember RFC4871 had an erratum about this that I think we fixed
in RFC6376, but I'll have to go back and double-check later this evening.
So if someone could capture that, it would be helpful.
I asked one of the original DKIM developers about this (who also maintains their own DKIM library) and he said:
Can you capture a copy of the canonicalized header and body of a message
that goes through that software? Seeing the original message and the raw
data that went through the hash will help.
I seem to remember RFC4871 had an erratum about this that I think we fixed
in RFC6376, but I'll have to go back and double-check later this evening.
So if someone could capture that, it would be helpful.