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

Results forwebmail.whm2-test.dev.mailchannels.net

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-07-29T02:57:09.873	2021-07-29T00:00:00	2021-10-27T23:59:59	whm2-test.dev.mailchannels.net	webmail.whm2-test.dev.mailchannels.net	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2021-07-29T02:57:09.873	2021-07-29T00:00:00	2021-10-27T23:59:59	whm2-test.dev.mailchannels.net	whm2-test.dev.mailchannels.net	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2021-07-29T02:57:08.841	2021-07-29T00:00:00	2021-10-27T23:59:59	whm2-test.dev.mailchannels.net	webmail.whm2-test.dev.mailchannels.net	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"
2021-07-29T02:57:08.841	2021-07-29T00:00:00	2021-10-27T23:59:59	whm2-test.dev.mailchannels.net	whm2-test.dev.mailchannels.net	C=US, ST=TX, L=Houston, O="cPanel, Inc.", CN="cPanel, Inc. Certification Authority"