Catch more ascii encoding errors to improve resilience against bad data

(LP: #1844189)

dkimpy_milter/__init__.py

@@ -305,6 +305,8 @@ class dkimMilter(Milter.Base):
                 self.dkim_comment = str(x)
                 if milterconfig.get('Syslog'):
                     syslog.syslog("check_dkim: {0}".format(x))
+            if not self.header_a:
+                self.header_a = 'rsa-sha256'
             if res:
                 if (milterconfig.get('Syslog') and
                         (milterconfig.get('SyslogSuccess') or
@@ -324,14 +326,20 @@ 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:
                 result = 'fail'
             res = False
-            self.arresults.append(
+            if self.header_d:
-                authres.DKIMAuthenticationResult(result=result,
+                self.arresults.append(
+                    authres.DKIMAuthenticationResult(result=result,
                                                  header_i=self.header_i,
                                                  header_d=self.header_d,
                                                  header_a=self.header_a,