Improve support of email importer if headers are missing

Fix #88

misp_modules/modules/import_mod/email_import.py

@@ -48,31 +48,38 @@ def handler(q=False):
                     "types": ['email-header']})
 
     # E-Mail MIME Boundry
+    if message.get_boundary():
         results.append({"values": message.get_boundary(),
                         "types": ['email-mime-boundary']})
 
     # E-Mail Reply To
+    if message.get('In-Reply-To'):
         results.append({"values": message.get('In-Reply-To').strip(),
                         "types": ['email-reply-to']})
 
     # X-Mailer
+    if message.get('X-Mailer'):
         results.append({"values": message.get('X-Mailer'),
                         "types": ['email-x-mailer']})
 
     # Thread Index
+    if message.get('Thread-Index'):
         results.append({"values": message.get('Thread-Index'),
                         "types": ['email-thread-index']})
 
     # Email Message ID
+    if message.get('Message-ID'):
         results.append({"values": message.get('Message-ID'),
                         "types": ['email-message-id']})
 
     # Subject
+    if message.get('Subject'):
         results.append({"values": message.get('Subject'),
                         "types": ['email-subject']})
 
     # Source
     from_addr = message.get('From')
+    if from_addr:
         results.append({"values": parseaddr(from_addr)[1],
                         "types": ['email-src'],
                         "comment": "From: {0}".format(from_addr)})
@@ -82,6 +89,7 @@ def handler(q=False):
 
     # Return Path
     return_path = message.get('Return-Path')
+    if return_path:
         # E-Mail Source
         results.append({"values": parseaddr(return_path)[1],
                         "types": ['email-src'],
@@ -96,7 +104,7 @@ def handler(q=False):
     recipient_headers = ['To', 'Cc', 'Bcc']
 
     for hdr_val in recipient_headers:
-        try:
+        if message.get(hdr_val):
             addrs = message.get(hdr_val).split(',')
             for addr in addrs:
                 # Parse and add destination header values
@@ -110,15 +118,12 @@ def handler(q=False):
                                 "comment": "{0}: {1}".format(hdr_val,
                                                              addr)})
 
-        except AttributeError:
-            continue
-
     # Get E-Mail Targets
     # Get the addresses that received the email.
     # As pulled from the Received header
     received = message.get_all('Received')
+    if received:
         email_targets = set()
-    try:
         for rec in received:
             try:
                 email_check = re.search("for\s(.*@.*);", rec).group(1)
@@ -130,8 +135,6 @@ def handler(q=False):
             results.append({"values": tar,
                             "types": ["target-email"],
                             "comment": "Extracted from email 'Received' header"})
-    except TypeError:
-        pass  # If received header is missing we can't iterate over NoneType
 
     # Check if we were given a configuration
     config = request.get("config", {})