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For various reasons I won't go into I've set up a custom DNS server for a delegated subdomain of my main domain. This DNS server is a .NET application which uses the ARSoft DNS library to respond to requests. This DNS server is working fine for A, CNAME and TXT records, but it doesn't seem to respond to MX requests when they have been forwarded from other popular open DNS servers. NSLOOKUP responds with the message "google-public-dns-a.google.com can't find cloud.xibis.net: Server failed" but if I use another DNS server like dns.xibis.com (the delegated subdomain DNS server) it works fine.

Here is a link to the output of the dig tool for the request:

https://www.digwebinterface.com/?hostnames=cloud.xibis.net&type=MX&showcommand=on&stats=on&trace=on&ns=resolver&useresolver=8.8.4.4&nameservers=

(Click 'Dig' to proceed)

You can clearly see at the bottom of the trace output that my DNS server is responding with the MX records, but the Google DNS server won't forward them for some reason.

The reason I'm doing this is to set up this domain for use with GSuite/Gmail.

Does anyone have any suggestions as to why this might be happening?

Thanks!

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Thank you for including your actual domain.

Your have configured the following sub domain delegation for cloud.xibis.net:

cloud.xibis.net.    60  IN  NS  dns.xibis.com.

And you have the correct A record for dns.xibis.com. as well:

dns.xibis.com.      60  IN  A   104.47.165.245

And when you query your MX records directly on the authoritative name server with dig MX cloud.xibis.net. @104.47.165.245 you get a response:

.           3600    IN  MX  1 ASPMX.L.GOOGLE.COM.
.           3600    IN  MX  5 ALT1.ASPMX.L.GOOGLE.COM.
.           3600    IN  MX  5 ALT2.ASPMX.L.GOOGLE.COM.
.           3600    IN  MX  10 ASPMX2.GOOGLEMAIL.COM.
.           3600    IN  MX  10 ASPMX3.GOOGLEMAIL.COM.

But that is not a correct response.

The expected and required results should not be only a leading dot but at that position your domain name is required. Responses should look like:

cloud.xibis.net.  3600  IN  MX  1 ASPMX.L.GOOGLE.COM.

That seems like a configuration error.

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  • Thank you, that appears to have solved it. I was following the instructions from Google which state to use @ or blank for the alias, but neither worked. support.google.com/a/answer/140034?hl=en
    – Ian Newson
    May 20, 2019 at 14:31
  • @ or a blank instead of an explicit resource record are shorthand used in zone files. It depends on the implementation if and how such entries are supported.
    – HBruijn
    May 20, 2019 at 14:53

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