ns-tmtr.verizon.com has no MX records.
Question and response
Question
dig ns-tmtr.verizon.com. MX
Answer
The response has no answer records.
Authority
verizon.com. 900 SOA ns-tmtr.verizon.com. sysmgr.verizon.com. 4905 900 600 4838400 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0