[bug] fix extraction of uuid from message headers

Before this commit, the mail receiver system used to compare the domain of the
delivery addresses found in the "Delivered-To" header to find out the final
delivery address. If we assume that the mail server delivery to the spool mail
directory was correct, then we have two facts: (1) the topmost "Delivered-To"
header is the one that indicates the correct final delivery address; and (2)
we should expect the address to be <uuid>@<domain> because of the earlier
alias resolve query made by the mail server.

Another problem is that the domain comparison would compare whatever is in the
"Delivered-To" header with whatever the python's socket module would return,
which depends on the values on /etc/hosts and the order of the values in that
file. This was causing problems whenever the platform made changes in
/etc/hosts.

So this commit eliminates the domain check and gets the uuid from the first
"Delivered-To" header found in the message.

Related: #6858.

1 files changed, 9 insertions, 13 deletions

diff --git a/src/leap/mx/mail_receiver.py b/src/leap/mx/mail_receiver.py
index f0b9c03..6b384f2 100644
--- a/src/leap/mx/mail_receiver.py
+++ b/src/leap/mx/mail_receiver.py
@@ -39,7 +39,6 @@ import signal
 
 import json
 import email.utils
-import socket
 
 from email import message_from_string
 from email.MIMEMultipart import MIMEMultipart
@@ -181,8 +180,6 @@ class MailReceiver(Service):
         self._directories = directories
         self._bounce_from = bounce_from
         self._bounce_subject = bounce_subject
-
-        self._domain = socket.gethostbyaddr(socket.gethostname())[0]
         self._processing_skipped = False
 
     def startService(self):
@@ -357,7 +354,7 @@ class MailReceiver(Service):
 
     def _get_owner(self, mail):
         """
-        Given an email, returns the uuid of the owner.
+        Given an email, return the uuid of the owner.
 
         :param mail: mail to analyze
         :type mail: email.message.Message
@@ -365,18 +362,17 @@ class MailReceiver(Service):
         :returns: uuid
         :rtype: str or None
         """
-        uuid = None
-
+        # we expect the topmost "Delivered-To" header to indicate the correct
+        # final delivery address. It should consist of <uuid>@<domain>, as the
+        # earlier alias resolver query should have translated the username to
+        # the user id. See https://leap.se/code/issues/6858 for more info.
         delivereds = mail.get_all("Delivered-To")
         if delivereds is None:
+            # XXX this should not happen! see the comment above
             return None
-        for to in delivereds:
-            name, addr = email.utils.parseaddr(to)
-            parts = addr.split("@")
-            if len(parts) > 1 and parts[1] == self._domain:
-                uuid = parts[0]
-                break
-
+        final_address = delivereds.pop(0)
+        _, addr = email.utils.parseaddr(final_address)
+        uuid, _ = addr.split("@")
         return uuid
 
     @defer.inlineCallbacks