mx-in.g.apple.com has no MX records.
Question and response
Question
dig mx-in.g.apple.com. MX
Answer
The response has no answer records.
Authority
g.apple.com. 300 SOA a.gslb.aaplimg.com. hostmaster.apple.com. 1715723413 1800 300 60480 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0