mx1.pulsesmtp.com has no MX records.
Question and response
Question
dig mx1.pulsesmtp.com. MX
Answer
The response has no answer records.
Authority
pulsesmtp.com. 10800 SOA a.dns.gandi.net. hostmaster.gandi.net. 1768125027 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0