B4J Question SMTP send as text and html

It is possible but you will need to build the mail structure yourself.

You can see an example of creating a mail message in MailCreator class: https://www.b4x.com/android/forum/threads/b4x-sending-emails-with-gmail-rest-api.81736/#content

In your case you need to create two parts. One with text/html and one with text/plain.

You can then send it as a plain text message and set the Content-Type header manually in the AdditionalHeaders map.