Mail server, why there is need in smtp.mail.com or imap.mail.com or mail.mail.com

Question

I'm trying to understand why we need this subdomains ?

(smtp.mail.com or imap.mail.com or mail.mail.com)

Do they point to same IP ? If yes why not to use FQDN ?

Or they point to a different IP ? when you need to implement this?

Answer 1

SMTP and IMAP are two different protocols, usually implemented by two different server software systems. On smaller deployments, they are often hosted on the same server, in which case the names are redundant.

On much larger deployments (say gmail or yahoo), they are hosted on separate servers, or sometimes on separate groups of servers, using multi-record DNS or a load balancer or even more exotic systems.