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

Results forwebmail.visitor.corpseed.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-02-28T04:13:44.201	2020-02-28T00:00:00	2020-05-28T23:59:59	visitor.corpseed.com	webmail.visitor.corpseed.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2020-02-28T04:12:22.661	2020-02-28T00:00:00	2020-05-28T23:59:59	visitor.corpseed.com	webmail.visitor.corpseed.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2020-02-08T03:22:34.204	2020-02-08T00:00:00	2020-05-08T23:59:59	visitor.corpseed.com	webmail.visitor.corpseed.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2020-02-08T03:22:14.709	2020-02-08T00:00:00	2020-05-08T23:59:59	visitor.corpseed.com	webmail.visitor.corpseed.com	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"