ProtonMail : file “catch all” messages into their own folder

ProtonMail’s Pro and Visionary plans let you configure a “catch all” address. All emails sent to the domain will end up in that address’s account. However, they all end up in your account’s inbox unless you set up a filter to file them into a special folder as described below.

If you don’t know what a “catch all” is, please see ProtonMail’s official doc on the subject : https://protonmail.com/support/knowledge-base/catch-all/

1. Create an address dedicated to catchall on you custom domain. (see ProtonMail doc) For example “catchall@domain.tld”.
2. Set the new address to be the catchall address.
   Go to the settings for your account and to the “Domains” section. Click the “catch-all” checkbox next to the address you created.
3. Create a folder for the caught messages. For example “catchall”.
4. Add a sieve filter to file the messages.
   1. Go to the settings for you account and to the “Filters” section.
   2. Add a Sieve filter by clicking the “Add Sieve filter” button.
   3. Give you filter a name, then replace the code with the one provided below.
   4. Don’t forget to “replace catchall@mydomain.tld” with the actual email address you created earlier, and “myfolder” by the name of the actual folder you created.
   5. Save the filter.

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

# File catchall messages into folder
if header:is "Delivered-To" "catchall@mydomain.tld" {
  fileinto "myfolder";
}

If you want to learn more about writing your Sieve filters scripts in ProtonMail, check out the docs.