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

Results forwww.mail.redkangaroo.net.ni

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-02-03T17:51:48.524	2016-01-07T23:39:38	2017-01-07T23:04:38	mail.redkangaroo.net.ni	www.mail.redkangaroo.net.ni	C=US, ST=Arizona, L=Scottsdale, O="Starfield Technologies, Inc.", OU=http://certs.starfieldtech.com/repository/, CN=Starfield Secure Certificate Authority - G2
2018-02-03T05:24:59.036	2015-11-24T22:13:38	2015-12-12T16:18:29	mail.redkangaroo.net.ni	www.mail.redkangaroo.net.ni	C=US, ST=Arizona, L=Scottsdale, O="Starfield Technologies, Inc.", OU=http://certs.starfieldtech.com/repository/, CN=Starfield Secure Certificate Authority - G2
2016-03-08T00:10:17.093	2015-01-14T00:00:00	2015-04-14T23:59:59	mail.redkangaroo.net.ni	www.mail.redkangaroo.net.ni	C=GB, ST=Greater Manchester, L=Salford, O=COMODO CA Limited, CN=COMODO RSA Domain Validation Secure Server CA