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

Results forwebmail.doublebug.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2019-01-27T22:14:58.315	2019-01-27T00:00:00	2019-04-27T23:59:59	doublebug.com	webmail.doublebug.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2019-01-27T22:14:44.173	2019-01-27T00:00:00	2019-04-27T23:59:59	doublebug.com	webmail.doublebug.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2018-10-27T22:11:52.662	2018-10-27T00:00:00	2019-01-25T23:59:59	doublebug.com	webmail.doublebug.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2018-10-27T22:11:33.857	2018-10-27T00:00:00	2019-01-25T23:59:59	doublebug.com	webmail.doublebug.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"