Hi I have bought a domain name, lets say example.com and I needed to set a wildcard subdomain on the DNS in order to each user of the website to have his own subdomain. I have created an email account on the server, lets say cutopus@cutop.us in order to let users contact the staff of the website.
Now, If I send email from the server using sendmail with contact@example.com as sender address, for example, the email delivers correctly, but If I want to send an email to cutopus@cutop.us the email does not get delivered.
My DNS records are as follows:
A @ 51.255.108.205 Automatic
A mail.cutop.us 51.255.108.205 Automatic
CNAME * cutop.us Automatic
MX cutop.us mail.cutop.us 10 Automatic
Using the following command:
dig cutop.us
I get the following output:
; <<>> DiG 9.8.3-P1 <<>> cutop.us
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41051
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;cutop.us. IN A
;; ANSWER SECTION:
cutop.us. 1798 IN A 51.255.108.205
;; Query time: 483 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri May 6 11:04:30 2016
;; MSG SIZE rcvd: 42
And using the following command:
dig MX cutop.us
I get the following output:
; <<>> DiG 9.8.3-P1 <<>> MX example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61642
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;cutop.us. IN MX
;; AUTHORITY SECTION:
cutop.us. 1799 IN SOA dns1.registrar-servers.com. hostmaster.registrar-servers.com. 2016050501 43200 3600 604800 3601
;; Query time: 486 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri May 6 11:06:43 2016
;; MSG SIZE rcvd: 99
Now the question is, why I cannot send emails to cutopus@cutop.us
The reason that you cannot email bob@example.com is that you only have an MX record configured for the address bob@cut.op.example.com in order to have mail delivered to example.com you need to have an MX record of
MX @ mail.cutop.us 10
unfortunately you will then have an issue with the rules of DNS, which forbid a CNAME record where another record exists.
If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different. This rule also insures that a cached CNAME can be used without checking with an authoritative server for other RR types.
Basically you can't have a Wildcard record and an MX record at the same level.