mail.mmsc.iristel.com has no MX records.
Question and response
Question
dig mail.mmsc.iristel.com. MX
Answer
The response has no answer records.
Authority
mmsc.iristel.com. 86400 SOA pdns104.ultradns.com. tldadmin.iristel.com. 2020070108 86400 86400 86400 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0