Custom Domain

Add custom domain according to https://proton.me/support/custom-domain is quite straight forward.

Sieve Filter

At https://account.proton.me/u/0/mail/filters you can add Sieve filters.

A good how to to be found at https://lugh.ch/protonmail-tricks.html.

E.g. you can move to spam mails according to X-Pm-Spamscore

require ["include", "environment", "variables", "relational", "comparator-i;ascii-numeric", "spamtest"];
require "fileinto";

# Generated: Do not run this script on spam messages
if allof (environment :matches "vnd.proton.spam-threshold" "*",
spamtest :value "ge" :comparator "i;ascii-numeric" "${1}")
{
    return;
}

if header :value "gt" :comparator "i;ascii-numeric" "X-Pm-Spamscore" "5" {
  fileinto "spammy";
}