Hi,

heirloom-mailx tries to recode the mail body and attachments to a minimum
encoding which can represent the used characters. While this is lets say
"unexpected" in case of the mail body it is utterly broken for attachments.

Sending cryptographically signed messages as an attachments breaks the
signature when the signed message contains utf-8 characters which can be
represented in iso-8859-1.

The default (either in code or config) should work out of the box at least
for attachments not beeing recoded.

Flo