I have been on the emailing lists of 2 forums (one of which is CodeProject), opting to receive notifications of posted answers to my questions, and I had no problem receiving their messages until a few weeks ago, when the messages stopped showing up.
I searched everywhere—All Mail, Spam, Trash: nothing.
I have only 3 filters set up in my Gmail account: these are for not having incoming mail from 3 email addresses (which do not include the email addresses of those 2 forums in question) sent to Spam.