Catch more ascii encoding errors to improve resilience against bad data

(LP: #1844189)

dkimpy_milter/__init__.py

@@ -324,7 +324,12 @@ class dkimMilter(Milter.Base):
                         syslog.syslog('DKIM: Fail (saved as {0})'
                                       .format(fname))
                 else:
-                    syslog.syslog('DKIM: Fail ({0})'.format(d.domain.lower()))
+                    if milterconfig.get('Syslog'):
+                        if d.domain:
+                            syslog.syslog('DKIM: Fail ({0})'
+                                          .format(d.domain.lower()))
+                        else:
+                            syslog.syslog('DKIM: Fail, unextractable domain'
             if res:
                 result = 'pass'
             else: