[Users] All mail folder filled by outgoing message successive versions

[Pierre A.]

Dear Claws Mail users,

on one account, IMAP Gmail, after sending a message, I see in 'All Mail' folder, besides the sent message, a list of successive states of the message before it was sent, about one per minute while working on the message.

The same is visible on the webmail.

Probably some backup mechanism running afoul. 

Fortunately, only the final version is sent.

Before doing further research, I am begging for quick advice.