gmp.fad.uncuyo.edu.ar has no MX records.
Question and response
Question
dig gmp.fad.uncuyo.edu.ar. MX
Answer
gmp.fad.uncuyo.edu.ar. 5 CNAME chasqui.fad.uncuyo.edu.ar.
Authority
fad.uncuyo.edu.ar. 5738 SOA ns1.fad.uncuyo.edu.ar. root.fad.uncuyo.edu.ar. 202312197 300 86400 2419200 604800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0