Invalid MX Records from notification.skype.com ?

morten444
morten444 used Ask the Experts™
on
Hi
We are using ISP Spamfilter where we have setup a rule that if a domain has an invalid MX Record, it should be seen as spam. I think that is very normal

Today we have started to get the first complaints..

A user gets a mail from xxx@skype.com and they get the mail
Same user after buying a product gets a confirmation mail from xxx@notification.skype.com but never gets the mail.

I then go through our log files and I can see the mail has ended up in spamfilter and the reason is
"invalid MX Record"

My question is: they are both comming from skype.com so why is one no MX record and has.
Is MX Record just defined by top domain?

I am asking to make sure that its not our spamfilter that is not set correct as I find it hard to belive skype does not have control over their MX Records

Any comment to confirm where the fault is are welcome
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
skype.com does not have any MX records by the look of it.  This is not necessarily surprising, big companies use different domains for different purposes.  However, this does force recipient mail servers to look for other ways to determine if their email are legit.  One way to do this is SPF.  The SPF record for skype.com is 62.221.20.26  So if you check your original email (the one that came through), my hunch is that it came from 62.221.20.26.  

Also, if you check Reverse DNS for 62.221.20.26 you will see it has skype.com in its text, so it is humanly possible to check legitmacy of the source.

The notification email didn't come through because there is no way to look it up, other than by chopping the domain part of the email address up to extract the skype.com part, then either (1) checking that for its' SPF record, or (2) looking at the PTR for 62.221.20.26 (the address presumably it was sent from) and determining that it is skype.com.  

The other possibility is that the mail didn't come from 62.221.20.26 at all.  If this is the case then it is a configuration error on Skype's part and therefore not surprised it got rejected.

The best workaround I can think of is to Whitelist notification.skype.com, or, preferably the IP that that notif came from.  I would not recommend Whitelisting skype.com as this will let the spammers in.

Author

Commented:
Hi
Thanks. We will switch off the MX record filtering and stick with the SPF and Reverse DNS

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial