How did mail come from [email protected]?

Question

CMS

I uploaded CSM Livestreet to the hosting, I did not change the mail in the [email protected] template, I thought that the mail simply would not come, I planned to figure it out later.
And she bang and came with the address "from: Postman Your Site [email protected]"
This is some kind of cheat, can I write any mail and will it be sent from it? Can I register someone else's mail? How did it work?
In gmaile, however, the following line is still visible from above: "[email protected] via lik.from.sh"

Answer 1

If you look at how the mail is sent, then everything will become clear.
The client connects to the server, sends a letter through its as. The server forwards to the recipient's server, where it indicates from whom. In fact, if you have your own server, you can write anything.
But in fact, in 99% of cases this does not work, because the recipient's servers will check the address using DNS.

Answer 2

Okey, google, "email sender spoofing".