Same here with dkimpy-milter 1.2.1-1~bpo10+1 (upstream is at 1.2.2), but I didn't manage to get a sample of that invalid looking email yet:
postfix/smtpd[1872437]: 818E75FD3A: client=XXX[XXX] postfix/cleanup[1872438]: 818E75FD3A: message-id=<XXX> dkimpy-milter[1846888]: UnicodeDecodeError: 'utf-8' codec can't decode byte 0x92 in position 5: invalid start byte dkimpy-milter[1846888]: dkimpy-filter: milter claimed not to reply in state 7 but did anyway 4
