It is very annoying to have to use the web frontend if I want to send an encrypted e-mail to a non-protonmail user. I mainly use Thunderbird and would be happy, if this encryption feature with password would be reachable via plugin from Thunderbird or Outlook. As a consultant I also know from a bunch of business users, that they would be happy to use protonmail if they transparently could use that feature with Thunderbird or Outlook.
So please make it happen :) As developer, I am happy to offer to help with the implementation.