With Proton and SimpleLogin you can effectively reply through all the aliases. It’s not actually unlimited addresses but I’ve been using it for some time and I find it meets all my needs in a simple clean way. Very happy with the combo.
That makes emails forwarded from, say, PayPal or ebay marked as scam/phishing in Gmail, AND makes it impossible to report actual spam that comes through.
With a well set up SRS all these emails are recognised correctly. SimpleLogin does some naïve forwarding which messes it up.
I'm migrating out of them exactly for this reason - if I could do it on my hobby server for my personal domains, THEY should be able to do it as well.