smtp.syncmail.net has no MX records.
Question and response
Question
dig smtp.syncmail.net. MX
Answer
The response has no answer records.
Authority
syncmail.net. 3600 SOA DNS101.REGISTER.COM. root.REGISTER.COM. 126021210 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0