It can be anything! An apex, subdomain, or even a URL.

Results fordata.themix.co.jp

Resolver

Location

MX

Name	TTL	Value
data.themix.co.jp	3600	10 data-themix-co-jp.mail.protection.outlook.com

Name	TTL	Value
data.themix.co.jp	3600	MS=ms64520546
data.themix.co.jp	3600	google-site-verification=eQrVlbbYBrLT-gLDxnTRn75H4fQSUU_fX4a-yDckpyI
data.themix.co.jp	3600	v=spf1 include:spf.protection.outlook.com include:one.zoho.jp ~all
data.themix.co.jp	3600	zoho-verification=zb81300395.zmverify.zoho.jp