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

Results forwebmail.dreadlocksbyrain.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-04-02T11:42:21.581	2020-04-02T10:42:21	2020-07-01T10:42:21	dreadlocksbyrain.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-04-02T11:42:21.444	2020-04-02T10:42:21	2020-07-01T10:42:21	dreadlocksbyrain.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-01-31T12:55:51.909	2020-01-31T11:55:51	2020-04-30T11:55:51	dreadlocksbyrain.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-01-31T12:55:51.683	2020-01-31T11:55:51	2020-04-30T11:55:51	dreadlocksbyrain.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-11-30T20:23:49.154	2019-11-30T19:23:48	2020-02-28T19:23:48	dreadlocksbyrain.willworland.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-11-30T20:23:48.923	2019-11-30T19:23:48	2020-02-28T19:23:48	dreadlocksbyrain.willworland.com	webmail.dreadlocksbyrain.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3