mails05.liveperson.net has no MX records.
Question and response
Question
dig mails05.liveperson.net. MX
Answer
The response has no answer records.
Authority
liveperson.net. 7200 SOA a1-175.akam.net. hostmaster.asia1.akam.net. 4138621300 14400 7200 1209600 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0