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

Results forwww.mail.zendesk.com

Resolver

Location

A

Name	TTL	Value
www.mail.zendesk.com	1800	216.198.53.2Zendesk, Inc. / Cloudflare London, LLC
www.mail.zendesk.com	1800	216.198.54.2Zendesk, Inc. / Cloudflare London, LLC

Name	TTL	Value
www.mail.zendesk.com	3600	10 mail.zendesk.com

Name	TTL	Value
www.mail.zendesk.com	3600	v=spf1 include:_netblocks.zdsys.com ~all