Dlaczego nie mogę uruchomić własnego serwera poczty e-mail Podobnie jak mój własny węzeł BTC?

But you can... Everything is about a having a own server - it can be vps, bare metal, dedicated server (you can buy such service), or even you can use your own computer. Most of e-mail services are installed on Linux servers and to do this admins use program (package) called Postfix or another one - Dovecot. Having own mailserver is kinda cool but it's very hard to maintain - you need to check logs, manage permissions, write new rules, do administer stuff :) In few words - it's not very hard to set it up but it need a lot of daily work and almost everyone want to outsource such a service.

Ależ możesz, kupujesz tani vps albo serwer dedykowany, instalujesz serwer pocztowy, podpinasz domeny etc. To jest bardziej pytanie czy potrzebujesz kupić browar aby napić się piwa.

kompletnie się na tym nie znam

Running your own email server requires a lot of technical knowledge and resources to ensure security, proper maintenance, and adherence to regulations. Unlike running a BTC node, which primarily involves validating transactions and contributing to the network's security, running an email server involves storing and transmitting sensitive personal and potentially confidential data. If not properly secured and maintained, your email server could be vulnerable to hacking and other security threats, potentially compromising the privacy and security of your emails and attachments. Additionally, many ISPs and email providers impose restrictions on running personal email servers due to concerns about spam, security breaches, and network abuse. So, while it is technically possible to run your own email server, it may not be practical or advisable for most individuals.