19.ff.e443.ip4.static.sl-reverse.com has no MX records.
Question and response
Question
dig 19.ff.e443.ip4.static.sl-reverse.com. MX
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0