According to a external lookup on your domain Code:
; <<>> DiG 9.4.2-P1 <<>> nkomail.se mx
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26165
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; QUESTION SECTION:
;nkomail.se. IN MX
;; ANSWER SECTION:
nkomail.se. 86367 IN MX 1 213.185.30.83.nkomail.se.
;; ADDITIONAL SECTION:
213.185.30.83.nkomail.se. 86367 IN A 213.185.30.83
so your server name should be 213.185.30.83.nkomail.se and not nkomail.se.