We had some trouble with our IMAP server. Because of that sometimes the copying process of send emails into the "Sent" folder didn't succeed. Our users did get an error message because of that. Sometimes even the draft was gone. They complained, that they had to write and send the email again. They didn't comprehend, that the email was indeed send, but they just could not see it in their "Sent" folder.

Because of that we want a send process, which either completes or fails as whole.
That means, that either the email is send AND is stored in "Sent", or nothing happenes and the unsuccessful email stays in "Drafts" (with an error message saying so).