mail.21grams.com has no MX records.
Question and response
Question
dig mail.21grams.com. MX
Answer
The response has no answer records.
Authority
21grams.com. 3600 SOA ns100.digicertdns.com. registry.ports.net. 2026021601 3600 900 1814400 3600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0