Tutanota (now just Tuta) allows you to use your domain. I use it, it doesn’t support external clients (Outlook, Thunderbird, etc.) but they do have Android, Linux, Windows (maybe Mac too) clients.

It’s also cheap.

I’ve been using it for a few years now, it works for me.

You can get a free account to check it out first and if you like it just upgrade to get the personal domain usage and increased storage limit.