Would it help if mail clients can be configured with a list of e-mail addresses or domains that are known to prefer plain text, and then automatically warn the

Would it help if mail clients can be configured with a list of e-mail addresses or domains that are known to prefer plain text, and then automatically warn the user and suggest to switch to plain text? Arguably such mail clients can come with a preconfigured, default list of well-known addresses or domains. That way the user doesn't have to go out of their way to find the plain-text/html switch. Another improvement is that mail clients implement a MarkDown or reStructuredText editing mode that will automatically generate a multipart message with both plain text and html parts. Is there any mail client like that out there?