mail.endstream.com has no CNAME records.
Question and response
Question
dig mail.endstream.com. NS
Answer
The response has no answer records.
Authority
endstream.com. 3282 SOA ns.endstream.net. hostmaster.endstream.net.endstream.com. 2026011201 14400 900 1800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0