What is your goal? Do you want to host your emails yourself? That's going to be a huge hassle. Best case scenario nobody accepts your mails because they suspect you're a spammer. Worst case scenario you get hacked and actually do send out spam.

You can also just switch to another email provider like proton. Then you don't have to deal with any of the stuff, except for giving all people and services your new address.

I imagine going through a "setup your own mail server guide" such as https://www.linuxbabe.com/mail-server/setup-basic-postfix-mail-sever-ubuntu will give you the basics or at least enough to allow you to ask the correct questions to get the answers you want.

It has short explanations of what the different DNS records do (A, MX, PTR, etc) and such woven into the guide.

(Have read you're not interested in self hosting - I think that's very sensible. It's a lot of work and even then, very difficult to do it well and be reliable)

Suggest finding a reputable email provider, and they will require payment.

I recently moved from gmail to proton. The migration process was very smooth, with proton copying over all my existing email and calendars from gmail. However, their web clients are very slow in comparison (since they're encrypted - click on an email and it's 3 seconds or so to open, an eternity!). I find that annoying enough that I've setup thunderbird via a proxy, but that has negated some of the ease of use.

There are quite a few good options around, maybe others will chip in with recommendations.

Once you have a new mail client, your user@gmail.com address will not be valid. However, if you want it to, you can keep your old email account with gmail as well, and have it forward all incoming email to your new home. That allows you to gradually move your accounts over at your own speed. I think this is important as there will be more than you expect of them, but the process isn't hard.

Most of those new providers will also allow you to use a personal domain, and multiple users. So you can register a domain that stays with you - that's the domain.org bit of your email address, and multiple users - the bit before the @.

The good providers will have guides and documentation about helping you through this also.

I don't have a book, but it's generally like this: providers offer you an email account. Usually, the provider also offers a website where you can access that email account ("webmail"). Some providers also offer mobile apps for access. Email accounts follow some standards, and almost all of them can be accessed via standard email clients (e.g. Thunderbird).

Most have a limited size for your account (e.g. 1GB) which has to fit all your attachments etc. If it's full, you can't receive more emails. Some have automated spam filters etc. Many are free, but their webmail usually contains ads.

In my opinion all that you need is a new mail provider/host of your choice and an own domain if you want to make future moving of mail providers easier.

Hosting an own mail server should not be your main focus when making an initial switch away from Gmail.

This: https://mwl.link/run-your-own-mail-server.html

I don't have this book by MWL, but, when I got my first Sysadmin job in 2015, I took over a network almost entirely run on FreeBSD, and I was gifted a couple of other books of his, in particular his ZFS volumes with Allan Jude, and I can say that his work is easy to read and good at giving you the most basic raw facts of the matter. If you really want to understand email, read this book and I guarantee you will get all the information you need.

I am not his marketer, just a person who was helped immensely by his work. He's on the Fedi as well, you can search in Mastodon.