repeated emails in sent box

I use Windows 7; Firefox and Hotmail. Over the last few days I have had the same 5 or 6 e-mails popping up regularly ( every 10 minutes or so) in my sent box. I have deleted the originals ( they were quite old) and all of the rogues, but they keep returning. The only new thing is I have a new phone, a Galaxy III. I can receive and send e-mails no problem but my sent box is full of theses repeats.As far as I know they are not actually being received by anyone as noone has complained to me. I do not use any other operating system for e-mail; I sign in using my hotmail details.