Enhancement: Sanity Check Subscribers MX Record

> admin(13907): ImportError: No module named DNS
> admin(13907): [----- Python Information -----]
> admin(13907): sys.version = 2.7.3 (default, Jan 2 2013, 13:56:14)
> [GCC 4.7.2]
> admin(13907): sys.executable = /usr/bin/python
> admin(13907): sys.prefix = /usr
> admin(13907): sys.exec_prefix = /usr
> admin(13907): sys.path = ['/usr/local/mailman-2.1.17/pythonlib', '/usr/local/mailman-2.1.17', '/usr/local/mailman-2.1.17/scripts', '/usr/local/mailman-2.1.17', '/usr/lib/python2.7/', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/lib/python2.7/site-packages']
> admin(13907): sys.platform = linux2
>
> AFAICS, it seems like Utils.py isn't locating the system wide python-dns
> library.

Correct. sys.path does not include /usr/lib/python2.7/dist-packages/

> How do I modify the sys.path to include python-dns under
> /usr/lib/python2.7/dist-packages?

sys.path.append('/usr/lib/python2.7/dist-packages/')

However, this should not be necessary as
'/usr/lib/python2.7/dist-packages/' should already be included in
sys.path. Why it isn't is a Python question, but
/usr/lib/python2.7/site.py which is normally executed during python
startup should put it there. What do you see if you invoke an
interactive python session and import sys and print sys.path as in

$ python
Python 2.7.5+ (default, Feb 27 2014, 19:37:08)
[GCC 4.8.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> print sys.path
['', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu',
'/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old',
'/usr/lib/python2.7/lib-dynload',
'/usr/local/lib/python2.7/dist-packages',
'/usr/lib/python2.7/dist-packages',
'/usr/lib/python2.7/dist-packages/PILcompat',
'/usr/lib/python2.7/dist-packages/gtk-2.0',
'/usr/lib/pymodules/python2.7',
'/usr/lib/python2.7/dist-packages/ubuntu-sso-client',
'/usr/lib/python2.7/dist-packages/ubuntuone-client',
'/usr/lib/python2.7/dist-packages/ubuntuone-control-panel',
'/usr/lib/python2.7/dist-packages/ubuntuone-storage-protocol']
>>>

--
Mark Sapiro <email address hidden> The highway is for gamblers,
San Francisco Bay Area, California better use your sense - B. Dylan

Hrmm,

dragon@quantum:/usr/local/mailman/Mailman
$ python
Python 2.7.3 (default, Jan 2 2013, 13:56:14)
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> print sys.path
['', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages', '/usr/lib/pymodules/python2.7']

I symlinked /usr/lib/python2.7/site-packages to /usr/lib/python2.7/dist-packages, since /usr/lib/python2.7/site-packages didn't exist on my install.

I ended up using python-dnspython 1.10.0-1, as it seems cleaner.

Here is what works for me now:

dragon@quantum:/usr/local/mailman/Mailman
$ diff Utils.py.org Utils.py
40a41
> import dns.resolver
237a239,246
> # MX Record sanity checks
> try:
> mx_domain = '.'.join(domain_parts)
> mx_query = dns.resolver.query(mx_domain)
> if len(mx_query) < 1:
> raise Errors.MMHostileAddress, s
> except:
> raise Errors.MMHostileAddress, s

Thanks for the assistance!

I adjusted my patch for the mailman-2.1.18-1 distribution, since that distribution requires dnspython as well for DMARC support.

I also corrected the lookup to search for MX records. Previous patch was searching A records incorrectly.

I also added user friendly error messaging for e-mail addresses being submitted with missing MX records.

Correct whitespace formatting...

The major issue with your patch is not all valid email domains have MX records. A valid email domain must have either an A record, an AAAA record or an MX record pointing to a host name with an A or AAAA record. E.g., a domain with an MX pointing to a host name with only a CNAME or MX is not a valid email domain, but a domain with only an A or AAAA record is a valid email domain. A domain which has a CNAME is a valid email domain as long as the CNAME directly or indirectly points to a host with an A, AAAA or MX as above. See RFC 5321, Sec 5.1.

Another issue is Mailman tries not to use bare except: clauses to catch exceptions. We prefer to catch only those explicit exceptions which might occur. I.e., in this case, explicitly only those exceptions that might be returned by dns.resolver.query.