microsoft has no MX records.
Question and response
Question
dig microsoft. MX
Answer
The response has no answer records.
Authority
microsoft. 3600 SOA dns1.nic.microsoft. hostmaster.nominet.org.uk. 1750680120 900 300 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0