CNAME of a DOMAIN name returns sometimes the soa and sometimes nothing, Why?

[news.csnet.nl]

My problem is that a domain i-55.com cannot send email to my domain csnet.nl
the response is nameserver time out.
I believe the nameserver for the i-55.com isn't setup right because if I ask
it something about i-55.com it claims not to be authoritive for that zone.
How ever that might be a side issue.

The mail software does a check for a the cname of i-55.com this doesn't
succeed and that gives a nameserver timeout.
why does a lookup for a  CNAME of a DOMAIN name returns sometimes the soa
and sometimes nothing?

e.g. dig  i-55.com cname  versus dig redhat.com cname


--------------------------i-55.com------------------------
; <<>> DiG 8.2 <<>> i-55.com cname
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 6
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUERY SECTION:
;;      i-55.com, type = CNAME, class = IN

----------------redhat.com--------------------------
; <<>> DiG 8.2 <<>> redhat.com cname
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUERY SECTION:
;;      redhat.com, type = CNAME, class = IN

;; AUTHORITY SECTION:
redhat.com.             1H IN SOA       ns.redhat.com. noc.redhat.com. (
                                        1999062200      ; serial
                                        1H              ; refresh
                                        30M             ; retry
                                        1W              ; expiry
                                        1H )            ; minimum