bill.ispsystem.net has no MX records.
Question and response
Question
dig bill.ispsystem.net. MX
Answer
The response has no answer records.
Authority
ispsystem.net. 900 SOA dns1.ispsystem.net. admin.ispsystem.com. 2026021608 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0