I need to restrict all new/create_account to only email addresses *@"protonmail.com" users. Do not want to allow pollution of system and other via gmail, or the rest. Could put it in Dolphin easy enough, but have not been able to discover how to incorporate the user message "Requires 'protonmail.com' email", and test to confirm *@"protonmail.com" address. All I find is path to page/create_account, but no folder for "page", or file create_account. Under Dolphin did not have to access and code on the actual page.
https://spnwo.com/ssl/una/page/create-account < "page/create-account" can not find folder or file.