Looks like it's "mail" and not "server1":
$ dig smartpremium.net MX
; <<>> DiG 9.10.4-P8-RedHat-9.10.4-5.P8.fc25 <<>> smartpremium.net MX
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6037
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 4
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;smartpremium.net. IN MX
;; ANSWER SECTION:
smartpremium.net. 604758 IN MX 10 mail.smartpremium.net.
;; AUTHORITY SECTION:
smartpremium.net. 172748 IN NS ns2.smartpremium.net.
smartpremium.net. 172748 IN NS ns1.smartpremium.net.
;; ADDITIONAL SECTION:
mail.smartpremium.net. 604758 IN A 162.210.250.181
ns1.smartpremium.net. 172748 IN A 162.210.250.181
ns2.smartpremium.net. 172748 IN A 162.210.250.181
;; Query time: 1 msec
;; SERVER: 129.240.2.27#53(129.240.2.27)
;; WHEN: Sun Sep 24 16:02:12 CEST 2017
;; MSG SIZE rcvd: 150