Hey, I noticed your most recent posts. It looks like you’re a beginner, and you have a lot of questions. That’s cool, but I think it would be a good idea for you to learn some fundamentals first, like (network layers, web application/network security, scripting, and basic computer exploitation). Once you understand how things work, you can explore more freely and find the resources you need for hands-on hacking.
There is no easy way to get a list of all email addresses via an email server.
You would have to test every conceivable combination of letters, which becomes difficult before the server blocks you. Also, there are two ways an email server accepts your requests. Either it checks every address you want to send to and rejects false ones (in which case you would get a response) or it takes the email and discards it afterwards.
It also rarely makes sense to want to have all email addresses. It would make more sense to find relevant addresses through social engineering. Job portals like Linkedin are very useful for this.