Ask HN: White-label webmail for secure business-to-customer communication

I'm looking for the traditional answer to secure "bank/hospital communication to customers/patients". (unfortunately pgp is not terribly practical in this use case) Basically you receive an email/text-message informing you that you have a message awaiting in the message center. You then get to login and see that the certificate is correct. Ideally it would be self-hosted, customizable, and possibly let customers pick a little icon unique to them (to try to alleviate phishing). So far I can't seem to find any quality product that fits the bill.