live.siteforce.com has no MX records.
Question and response
Question
dig live.siteforce.com. MX
Answer
The response has no answer records.
Authority
live.siteforce.com. 10 SOA dns01.salesforce.com. hostmaster.salesforce.com. 2018025560 600 900 2592000 10
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0