This bug only happens with linked Gmail account. Looks same as issue 3839? After sending email in Claws client the email in progress looks like it's been repeatedly sent to destination address at regular intervals of <1 min (rather than removing from gmail drafts which i assume is intended behavior it gets prepended as a thread in the [imap] sent folder). I ran a test by emailing another address I own and the issue seems to be only in how it's represented in gmail webclient thankfully. I had quite a shock when I thought I had spammed a formal work email with two dozen badly written drafts. Perhaps there could be a warning in interface or default behavior could be set to not forward drafts to imap? I nearly emailed an apology to destination, but luckily I checked first. Cheers
That's because gmail can't handle incremental auto-saving. You'll need to turn off the option 'Automatically save message to Drafts every [n] characters', found here: /Configuration/Preferences/Compose/Writing.
... Alternately, in your gmail account's prefs, set the Drafts folder to a local folder in an MH mailbox, (on the Advanced page of the account prefs).