new: Allow to disable DNS lookups

Fix #26

mail2misp/mail2misp.py

@@ -14,7 +14,11 @@ from pyfaup.faup import Faup
 from pymisp import PyMISP, MISPEvent, MISPObject, MISPSighting
 from pymisp.tools import EMailObject, make_binary_objects
 from defang import refang
-import dns.resolver
+try:
+    import dns.resolver
+    HAS_DNS = True
+except ImportError:
+    HAS_DNS = False
 
 
 def is_ip(address):
@@ -299,6 +303,7 @@ class Mail2MISP():
                         email_object.add_reference(attribute.uuid, 'contains')
                 else:
                     related_ips = []
+                    if HAS_DNS and self.config.enable_dns:
                         try:
                             syslog.syslog(hostname)
                             for rdata in dns.resolver.query(hostname, 'A'):