[bdNOG] Yahoo Mail can't communicate with my domain servers

Brian Candler brian at nsrc.org
Wed Dec 23 15:40:48 BDT 2015

Unfortunately the checker at dns.squish.net appears to be broken.

Trying this manually from here (UK):

$ dig +norec @a.root-servers.net. btraccl.net. mx
.. referral to gtld servers

$ dig +norec @a.gtld-servers.net. btraccl.net. mx
btraccl.net.            172800  IN      NS      ns1.btraccl.net.
btraccl.net.            172800  IN      NS      ns2.btraccl.net.

ns1.btraccl.net.        172800  IN      A
ns2.btraccl.net.        172800  IN      A

Ah: so your problem is that you are not following RFC 2182 (esp. 
sections 3.1 to 3.3). It is almost entirely pointless having two 
authoritative DNS servers if they are on the same subnet, for the very 
reason that you have discovered: the Internet is not a fully-connected 

Get your secondary service on a different network, on a different 
backbone AS and preferably in an entirely different country.

You may be able to find a similar-sized organisation in a different 
country which is happy to swap secondary DNS service with you (i.e. they 
act as your secondary, and vice versa). Otherwise, you can take a cheap 
commercial DNS service (e.g. Godaddy Premium DNS). Or, if you already 
have a cloud VM somewhere with a static IP (e.g. EC2 with Elastic IP) 
you can run your secondary DNS on that.

Of course, if Yahoo cannot contact either of your DNS servers, and your 
mail server is on the same subnet (, then they're still 
not going to be able to send mail to you. But at least the name will be 
resolved, and you will get a more useful error message, and you can take 
up the lack of SMTP connectivity separately.

Furthermore: if you have a remote VM under your control, you can make 
this a secondary MX receiver for your domain, so that people who cannot 
deliver mail directly to you will deliver to your secondary MX, which in 
turn will relay to your main mail server.



More information about the nog mailing list