fix: update mailer.py (#342)

integrations/mailer/mailer.py

@@ -406,6 +406,13 @@ def validate_rules(rules):
                                 rule, key)
                     valid = False
                     break
+            try:
+                re.compile(field['regex'])
+            except re.error:
+                LOG.warning('Invalid rule %s, regex %s is not legal',
+                            rule, field['regex'])
+                valid = False
+                break
         if valid is False:
             continue