diff -rupN mailman-2.1.18-1.org/Mailman/Cgi/admin.py mailman-2.1.18-1/Mailman/Cgi/admin.py
--- mailman-2.1.18-1.org/Mailman/Cgi/admin.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Cgi/admin.py	2015-02-15 00:22:05.000000000 -0800
@@ -1408,6 +1408,9 @@ def change_options(mlist, category, subc
             except Errors.MMHostileAddress:
                 subscribe_errors.append(
                     (safeentry, _('Hostile address (illegal characters)')))
+            except Errors.MMEmailMissingMXRecord:
+                subscribe_errors.append(
+                    (safeentry, _('Email address missing DNS MX record')))
             except Errors.MembershipIsBanned, pattern:
                 subscribe_errors.append(
                     (safeentry, _('Banned address (matched %(pattern)s)')))
diff -rupN mailman-2.1.18-1.org/Mailman/Cgi/options.py mailman-2.1.18-1/Mailman/Cgi/options.py
--- mailman-2.1.18-1.org/Mailman/Cgi/options.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Cgi/options.py	2015-02-15 00:19:33.000000000 -0800
@@ -410,6 +410,8 @@ address.  Upon confirmation, any other m
                 msg = _('Bad email address provided')
             except Errors.MMHostileAddress:
                 msg = _('Illegal email address provided')
+            except Errors.MMEmailMissingMXRecord:
+                msg = _('Email address provided missing DNS MX record')
             except Errors.MMAlreadyAMember:
                 msg = _('%(newaddr)s is already a member of the list.')
             except Errors.MembershipIsBanned:
diff -rupN mailman-2.1.18-1.org/Mailman/Cgi/subscribe.py mailman-2.1.18-1/Mailman/Cgi/subscribe.py
--- mailman-2.1.18-1.org/Mailman/Cgi/subscribe.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Cgi/subscribe.py	2015-02-15 00:42:45.000000000 -0800
@@ -214,6 +214,10 @@ The email address you supplied is not va
         results = _("""\
 Your subscription is not allowed because the email address you gave is
 insecure.""")
+    except Errors.MMEmailMissingMXRecord:
+        results = _("""\
+Your subscription is not allowed because the email address you gave
+does not have a DNS MX record.""")
     except Errors.MMSubscribeNeedsConfirmation:
         # Results string depends on whether we have private rosters or not
         if privacy_results:
diff -rupN mailman-2.1.18-1.org/Mailman/Commands/cmd_subscribe.py mailman-2.1.18-1/Mailman/Commands/cmd_subscribe.py
--- mailman-2.1.18-1.org/Mailman/Commands/cmd_subscribe.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Commands/cmd_subscribe.py	2015-02-15 00:23:58.000000000 -0800
@@ -125,6 +125,11 @@ Mailman won't accept the given email add
 Your subscription is not allowed because
 the email address you gave is insecure."""))
         return STOP
+    except Errors.MMEmailMissingMXRecord:
+        res.results.append(_("""\
+Your subscription is not allowed because
+the email address you gave does not have a DNS MX record."""))
+        return STOP
     except Errors.MMAlreadyAMember:
         res.results.append(_('You are already subscribed!'))
         return STOP
diff -rupN mailman-2.1.18-1.org/Mailman/Errors.py mailman-2.1.18-1/Mailman/Errors.py
--- mailman-2.1.18-1.org/Mailman/Errors.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Errors.py	2015-02-15 00:24:38.000000000 -0800
@@ -100,6 +100,10 @@ class MMHostileAddress(EmailAddressError
     """Email address has potentially hostile characters in it."""
     pass
 
+class MMEmailMissingMXRecord(EmailAddressError):
+    """Email address missing DNS MX record."""
+    pass
+
 
 # Exceptions for admin request database
 class LostHeldMessage(MailmanError):
diff -rupN mailman-2.1.18-1.org/Mailman/Utils.py mailman-2.1.18-1/Mailman/Utils.py
--- mailman-2.1.18-1.org/Mailman/Utils.py	2014-05-06 09:43:56.000000000 -0700
+++ mailman-2.1.18-1/Mailman/Utils.py	2015-02-15 00:48:58.000000000 -0800
@@ -243,6 +243,15 @@ def ValidateEmail(s):
     for p in domain_parts:
         if len(p) == 0 or p[0] == '-' or len(_valid_domain.sub('', p)) > 0:
             raise Errors.MMHostileAddress, s
+    # MX Record sanity test
+    if dns_resolver:
+        try:
+            mx_domain = '.'.join(domain_parts)
+            mx_query = dns.resolver.query(mx_domain, 'MX')
+            if len(mx_query) < 1:
+                raise Errors.MMEmailMissingMXRecord, s
+        except:
+            raise Errors.MMEmailMissingMXRecord, s