How to implement an email client for sending letters, with your own hands?

Question

Email

Let's say I want to send a letter from [email protected] to [email protected]? I have a domain name, will registering a domain on a mail service help me in this case, and with a letsencrypt certificate? I just painfully understand how many spammers on bots jam the work of mail services and what is the policy against them! In general, I will reformulate the question: "How to implement mail sending without financial costs?"

Answer 1

Without financial costs - Make yourself a mailbox on the same mail.ru or yandex.ru
and send letters through their web interface.

Answer 2

Something here "horses mixed up in a bunch, people ...". And here the domain name, and LE? If you want to send a letter from [email protected] to [email protected] - get yourself a mailbox [email protected] - and send it to your health. Everything will be done by mail.ru (and at the same time it will scan the mail, select postal addresses in order to sell them later, maybe they will notify the comrade major if he finds something interesting ...).
Or maybe you want to become a mail relay for delivering mail from [email protected] to [email protected]?