Thanks LeonidS, Wish could do it like in Dolphin. Much cleaner when you can NOTICE the user and give them a link to www.protonmail.com so they can create that before completing the Sign-UP part, and it tests for "@protonmail.com" and sends a rejection, retry, message if need be.
From other inquiries, that may be a good, helpful, needed function to code or design into the create-account code. Anyone there can do it, and how much? Shouldn't be that difficult, basically have 1 flag (use the feature or not) 2) enter in domain(s) (one or more) to accept or reject separated by comma.
Anyway, trust all is going well. Have a good week. Thanks again. Robert