Please examine the following setting: Settings > Account Settings > the account in which your problem occurs > Copies & Folders > "When sending messages, automatically:" > Is "Place replies in the folder of the message being replied to" checked or not? If it is not checked, then my post will not be helpful to you. If it is checked, then a copy of your reply will be put inside the same folder (e.g. "Inbox" folder) of the mail you replied, rather than inside "Sent" folder. I think the mail was indeed sent to the recipient when you clicked "Send" for the first time. The mail you saw in your "Inbox" folder was a copy of the mail you had just sent. When you "select that incoming email, go to the Message menu, select Edit as a new message, and send it straight away", I think you actually sent the mail for the second time. If you uncheck "Place replies in the folder of the message being replied to", then the mail you sent will be put inside "Sent" folder.