Apple Mail, producing multiple duplicate drafts on gmail Apple Mail is producing multiple duplicate drafts on gmail.

After I send a message, there are multiple drafts of it left :-(.

That totally kills productivity and confidence. As I see the leftover draft, I'm never sure if I did actually send the message or not.
Not having a draft == msg was sent, but not in this case.

I had a similar problem with my previous company IMAP server.

What is the cause and how can I fix it?

Are you guys/girls using Apple Mail with GMail?
I've seen this behavior using Apple Mail since macOS Sierra. I haven't found a workaround d yet, but I know the email is sent because there is a copy in my Sent folder. Once a week or so, I go into the Google Inbox (should work for classic GMail too) Drafts folder and delete the email threads that are marked "Draft". This clears up the duplicates from Apple Mail on next sync. 

My guess is Apple Mail, when saving drafts periodically to the server (Google) while one is drafting an email, is not using the right mechanism (API call) such that every draft version collapses into one on Google end. This incorrect mechanism results in each draft showing up as individual "drafts".