05 Aug

More about SPF records

Hello all!

Few days back I visited Official Google Apps forum (one of my favorite places 🙂 ) and answered many questions. It was quite after some time i was there and found few cases/questions/problems as really interesting.

Here’s one of the questions asked there by a admin named aol985 about SPF records.

Question image

His question –

As described in http://www.google.com/support/a/bin/answer.py?hl=en&answer=33786 , I set SPF record for mashfilm.ru domain to “v=spf1 include:aspmx.googlemail.com ~all”. But aspmx.googlemail.com currently does not resolves. Is it correct?

Nice one!

He is right on fact that aspmx.googlemail.com does NOT resolve. Ok why?

Thus no A record which means it won’t resolve, BUT one must remember that a zone can have many records working side by side offering their own feature, like – MX records can be there with/without A, same with txt records, and few other also.

Got it

Now observing the spf record by Google – “v=spf1 include:aspmx.googlemail.com ~all”

here include:aspmx.googlemail.com

means to include the spf record of aspmx.googlemail.com which makes sense as:

Now it means spf record for aspmx.googlemail.com is “v=spf1 redirect=_spf.google.com”

Now trying to understand _spf.google.com

underscore right in start makes it different from a sub-zone since it can’t be used as a domain but will still remain a working sub zone in terms of DNS.

So now since it can’t be used as a  sub domain i.e which can be used to be attached with web server and can supply pages via ftp, there is no meaning of A record for it here.

Checking txt string of _spf.google.com

And here we got it!

So much information in just one hostname!

so much

“v=spf1 ip4:216.239.32.0/19 ip4:64.233.160.0/19 ip4:66.249.80.0/20 ip4:72.14.192.0/18 ip4:209.85.128.0/17 ip4:66.102.0.0/20 ip4:74.125.0.0/16 ip4:64.18.0.0/20 ip4:207.126.144.0/20 ?all” is a part of SPF record which Google makes its Google Apps users to use.

Thus using

“v=spf1 include:aspmx.googlemail.com ~all” in spf tells that “this domain allows all of the server on this ip range – ip4:216.239.32.0/19 ip4:64.233.160.0/19 ip4:66.249.80.0/20 ip4:72.14.192.0/18 ip4:209.85.128.0/17 ip4:66.102.0.0/20 ip4:74.125.0.0/16 ip4:64.18.0.0/20 ip4:207.126.144.0/20 as authorized to send email on behalf of that domain.

bye

So that’s how spf works in this case. 🙂

[ratings]