loadbalancing MX records

[José M. Fandiño]

Hello,

I'm curious about this form of loadbalancing for
mail (MX):

; <<>> DiG 2.2 <<>> @who.cdrom.com tsai.es MX
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10
;; flags: qr rd ra; Ques: 1, Ans: 1, Auth: 3, Addit: 7
;; QUESTIONS
;;      tsai.es, type = MX, class = IN

;; ANSWERS:
tsai.es.        115493  MX      100 mail.infomail.tsai.es.

;; ADDITIONAL RECORDS:
mail.infomail.tsai.es.  106522  A       194.224.53.134
mail.infomail.tsai.es.  106522  A       194.224.53.135
mail.infomail.tsai.es.  106522  A       194.224.53.142
mail.infomail.tsai.es.  106522  A       195.235.39.6

if any "mail.infomail.tsai.es" host fail the message
will be lost?

is not better multiple MX definitions 
with equal preference?

regards,

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