The dmarc rule can throw TypeError resulting in a shunted message for certain malformed messages.
Parsing of a message with raw non-ascii characters in a header results in the header being RFC 2047 encoded as base64 with character set 'unknown-8bit'. This is not an issue per se, but when the parsed message object's get() method is called to retrieve the header, an email.header.Header object is returned rather than a string, and in the case of a From: header, the dmarc rule calls email.utils.parseaddr() on that result which throws the exception.
Edited by Mark Sapiro