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

Results forwebmail.innerg.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-05-12T13:36:31.824	2020-05-12T12:36:31	2020-08-10T12:36:31	webdisk.innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-05-12T13:36:31.652	2020-05-12T12:36:31	2020-08-10T12:36:31	webdisk.innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-04-19T12:15:54.008	2020-04-19T11:15:53	2020-07-18T11:15:53	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-04-19T12:15:53.866	2020-04-19T11:15:53	2020-07-18T11:15:53	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-17T13:32:34.361	2020-02-17T12:32:33	2020-05-17T12:32:33	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-02-17T13:32:33.786	2020-02-17T12:32:33	2020-05-17T12:32:33	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-12-17T19:01:59.848	2019-12-17T18:01:59	2020-03-16T18:01:59	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-12-17T19:01:59.708	2019-12-17T18:01:59	2020-03-16T18:01:59	innerg.com	webmail.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-02-02T03:05:42.98	2019-02-02T02:05:41	2019-05-03T02:05:41	innerg.com	*.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-02-02T03:05:41.931	2019-02-02T02:05:41	2019-05-03T02:05:41	innerg.com	*.innerg.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3