I’m not familiar with Mailbox, but I’ve recently switched to Proton with custom domains, and I’ve made use of their partnership with Simple Login for semi-custom domains and aliases on them. The rest is about that.

I think if you know you need more than 3 unique domains (that being the number offered in the Proton Unlimited plan), then maybe Mailbox is the move?

On security, I’m also a beginner, but from what I’ve read, I’ve decided to setup my addresses so that I’m never handing out an address that includes a stock Proton domain (e.g. @proton.me or @pm.me). I’m basically only using a Proton domain address to login to my Proton account, which collects emails from my custom domain addresses and Simple Login aliases.

Another thing. Setting up a catch-all email in Proton, which you seem to have done, allows any [email protected] address to login to your Proton account. If that is a security concern for you, then I recommend exploring the Simple Login partnership. My threat model has me generally creating one email address for each service I use. This allows me to maintain a single address for professional stuff and other addresses for everything else.

While your custom domain @name reveals your name, like you said, you’ll use it to engage with entities that expect you to relinquish some privacy. I recommend WHOIS protections for you domain if you’re not already doing that though.

I hope this is helpful for understanding your possible options with Proton, at least somewhat! Still on a learning journey myself :)