smtp03.mbxg.com has no MX records.
Question and response
Question
dig mbsrvlet.mbxg.com. MX
Answer
The response has no answer records.
Authority
mbxg.com. 3600 SOA dns01.donovandata.com. domainadmin.mediaocean.com. 2024080703 900 600 1209600 3600
Additional
. 0 OPT ; payload 1500, xrcode 0, version 0, flags 0