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

Results formail.mindtechnic.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2017-01-30T13:48:09.133	2017-01-28T00:00:00	2017-04-28T23:59:59	mindtechnic.com	mail.mindtechnic.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2016-11-17T23:47:04.748	2016-11-13T00:00:00	2017-02-11T23:59:59	mindtechnic.com	mail.mindtechnic.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2016-11-15T20:24:18.419	2016-11-10T00:00:00	2017-02-08T23:59:59	mindtechnic.com	mail.mindtechnic.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"