When I write emails in Thunderbird (currently version 60 but this goes back since long) I write them in HTML. I see all the markup buttons and it looks OK. Then I send them and suddenly they are converted to plain text.
When I reply to an HTML email, the reply is often in HTML, so that goes as expected.
I use several email accounts, Gmail, Exchange and provider pop/imap accounts. All accounts are set to create HTML emails. I can't seem to find the cause of this.
How can I set Thunderbird to always use HTML when creating new mails?