It is shocking that after moving from Google workspace to Proton as the back office for our professional email adresses etc, all the major Dutch institutions are blocking us as spam. All our contacts have to whitelist us individually. So I think we are forced to go back to Google, where we had this problem occasionally but not as massively as now. It seems the reason is that Microsoft, used by almost all institutions in NL, simply blocks all Proton mail .😈 ( DNS=OK configured)