mail.wisperisp.com has no MX records.
Question and response
Question
dig mail.wisperisp.com. MX
Answer
The response has no answer records.
Authority
wisperisp.com. 3600 SOA dns1.wisperisp.com. hostmaster.wisperisp.com. 2024013597 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0