Introductions List

>>> dkim = DKIM()
>>> dkim.add_frozen(DKIM.RFC5322_SINGLETON)
>>> [text(x) for x in sorted(dkim.frozen_sign)]
['cc', 'date', 'from', 'in-reply-to', 'message-id', 'references', 'reply-to', 'sender', 'to']
>>> dkim2 = DKIM()
>>> dkim2.add_frozen((b'date',b'subject'))
>>> [text(x) for x in sorted(dkim2.frozen_sign)]
['date', 'from', 'subject']

>>> dkim = DKIM()
>>> dkim.add_should_not(DKIM.RFC5322_SINGLETON)
>>> [text(x) for x in sorted(dkim.should_not_sign)]
['bcc', 'cc', 'comments', 'date', 'dkim-signature', 'in-reply-to', 'keywords', 'message-id', 'received', 'references', 'reply-to', 'resent-bcc', 'return-path', 'sender', 'to']