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

Results formail.pecchamber.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2017-04-17T20:12:08.565	2017-04-15T00:00:00	2017-07-14T23:59:59	pecchamber.com	mail.pecchamber.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2017-01-31T14:10:51.156	2017-01-29T00:00:00	2017-04-29T23:59:59	pecchamber.com	mail.pecchamber.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2016-11-17T00:10:52.976	2016-11-14T00:00:00	2017-02-12T23:59:59	pecchamber.com	mail.pecchamber.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"