o1.ptr5559.nifty.com has no MX records.
Question and response
Question
dig o1.ptr5559.nifty.com. MX
Answer
The response has no answer records.
Authority
nifty.com. 900 SOA odns0.nifty.ad.jp. hostmaster.nifty.ad.jp. 2026021703 3600 900 3600000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0