Send an Email to the user who is not associated with any record in Dynamics CRM

I have been seen a lot of people were asking for sending emails to an external user, who is not associated with either Contacts, Account, Queue, Lead, User or any CRM entity record.

Usually, If you put any email address in 'To' field, you see an error in the email address (see below):

CRM System Setting: Allow messages with unresolved email recipients to be sent

Cheers