By comparing logs for various runs, I can see that the error is not fatal. It just causes one log message to disappear. That's this one:
log.info( 'Attempting DKIM authentication of message id=%s from=%s sender=%s' % (signed_message['Message-ID'], signed_message['From'], signed_message['Sender']))
Looks like From/Sender may be non-ASCII bytestrings, and logging is trying to encode them to UTF-8?
By comparing logs for various runs, I can see that the error is not fatal. It just causes one log message to disappear. That's this one:
log.info( message[ 'Message- ID'],
signed_ message[ 'From'] ,
signed_ message[ 'Sender' ]))
'Attempting DKIM authentication of message id=%s from=%s sender=%s'
% (signed_
Looks like From/Sender may be non-ASCII bytestrings, and logging is trying to encode them to UTF-8?