>The problem is that you have no MX record setup in your DNS!!!
that's one pb, but MTA's should then try the A record, but there isn't one of those either:
# dig cdnet.com.mx a
; <<>> DiG 8.3 <<>> cdnet.com.mx a ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0 ;; QUERY SECTION: ;; cdnet.com.mx, type = A, class = IN
Len
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