mailer7.zenter.is has no MX records.
Question and response
Question
dig mailer7.zenter.is. MX
Answer
The response has no answer records.
Authority
zenter.is. 1800 SOA lia.ns.cloudflare.com. dns.cloudflare.com. 2395587190 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0