mx vs ns

[Mij]

$ dig ns @tld1.ultradns.net freebsd.org
;; ANSWER SECTION:
FREEBSD.ORG.            172800  IN      NS      NS2.DOWNLOADTECH.COM.
FREEBSD.ORG.            172800  IN      NS      NS1.IAFRICA.COM.
FREEBSD.ORG.            172800  IN      NS      NS1.DOWNLOADTECH.COM.
FREEBSD.ORG.            172800  IN      NS      NS0.FREEBSD.ORG.


$ dig mx @ns0.freebsd.org freebsd.org
;; ANSWER SECTION:
freebsd.org.            600     IN      MX      10 mx1.freebsd.org.
[ not rr ]

is it prudent to have 4 ns and just 1 mail exchanger?

bye