Do you mean buying your own domain, and forward email sent to it to an email provider?

A lot of email providers have that option (with paid plans). For example

https://proton.me/support/custom-domain

I recently bit the bullet and bought in to mxrouting’s lifetime account. 10GB, unlimited domains, unlimited accounts, “forever” (for the remainder of the time mxrouting exists) for the semi decent price of $100.

I like Mailinabox

You can use it in the cloud or fully self-host on your own hardware if you want. (Assuming your ISP allows this)

I host my own domain and DNS and point to a web hosted provider.

I was pretty happy with Proton mail, but moved because I wanted to provision more inboxes and the price per inbox didn't scale great, for me.

I needed something that allows for unlimited aliases as I'm creating an email address for every service I sign up to.

I'm using UberSpace for 5€ a month which also allows for hosting websites. Very happy with them.

I would go selfhosted and use a mai-in-a-box solution. Easy to setup, handles all the spam DNS settings etc and if you put it on an ip segment that is generally spammer-free, then you should have a fantastic solution (I habe used it myself for many years).