The state of email is disappointing and sad. It is possibly one of the most centralized decentralized protocols/networks on the planet. We need a good replacement for it. It's so legacy.
If you have set up a new system without any reputation now, even if you have set up DKIM and SPF, it's now a lot worse. Major providers like Google and Microsoft won't really tell you, but if you are new but don't have a dedicated AS and instead you're using (for example) Linode you'll be scored lower by having low-cost solutions that just so happens to be abused by spammers.
Still - if you self-host just assume at some point it will go down and you may have to deal with a backup restore before you can receive any more email. If that gets in the way of your life, you may want to reconsider :)
Source: Having own email server for 17 years. Absolutely happy with it. Again, that doesn't mean everyone should do it, but I'd abstain from advices like you should not! or should do same.
I do host mail for tens of domains and never had issues with deliverability.
So, what can I do to just keep a backup of all my emails (one @gmail.com and other personal website emails)?
Maybe for me, just having those emails accessible somewhere is more important (other than primary source/ provider)
Thanks
I have it setup as my.srv1.domain.com (with apps at appX.srv1.domain.com). This way if I need more apps I just spin up another 1G Ubuntu instance somewhere and install cloudron as srv2 etc, for another 2 apps that fit squarely into the 1G and also Cloudron free tier. Cloudron in their forum has also stated that this does not violate their terms (they said completely within terms).
Since almost all of the people you correspond with are sending from Gmail or Office365 or <insert other oligopoly provider>, there is no email security anyway. Sadly.
So I would probably avoid Amazon just because many of their services charge for data out. It isn't out, but it's a variable for you, and you probaly want something that's flat per month. Cheapest you are going to get with somewhat reliable service is either going to be Hetzner or BuyVM. Hetzner is better for someone who doesn't want to tinker, BuyVM for those who do (BuyVM is a little less reliable, but you can set it up cheaper if you are willing to do a little bit of manual work with shell commands).
Secondly, I'd suggest you host this through Cloudron. It helps you handle automatic security updates and backups. It's very nice, and worth paying for, although it's a little pricey for individuals.
Third, with email, you can host it yourself (in fact Cloudron has this built in), but I'm going to recommend against it, or at least recommend that you pipe important emails through another service like Fastmail. Let me explain why. There's going to be some point after hosting for 5 years, where your server is going to go down. Now email will be fine, it's built to deal with cases where servers go down, but... we rely so much on email right now, that it's going to really suck to have it down. So by all means, have your personal email come to the server, but keep anything that you can't do without running on a managed service. You can pipe it through your own domain, and set up automatic forwarding, but it's going to be a little better to run important stuff through someone else's server, imho.
Just my two (or three, I guess) cents.