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

Results forwebmail.davidjohn.pro

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-01-25T01:42:26.825	2020-01-25T00:42:26	2020-04-24T00:42:26	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-01-25T01:42:26.58	2020-01-25T00:42:26	2020-04-24T00:42:26	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-11-25T01:34:04.572	2019-11-25T00:34:04	2020-02-23T00:34:04	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-11-25T01:34:04.427	2019-11-25T00:34:04	2020-02-23T00:34:04	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-09-25T01:29:55.649	2019-09-25T00:29:55	2019-12-24T00:29:55	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-09-25T01:29:55.059	2019-09-25T00:29:55	2019-12-24T00:29:55	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-07-25T06:48:35.837	2019-07-25T05:48:35	2019-10-23T05:48:35	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2019-07-25T06:48:35.31	2019-07-25T05:48:35	2019-10-23T05:48:35	davidjohn.pro	webmail.davidjohn.pro	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3