iCloud Storage and Back up

My iCloud Storage states that Mail is at 17.1mb. I have deleted all inbox,sent, junk (apart from last 2 months) for all of my email accounts (I rarely use my @me.com) both on my iPhone and within Outlook on my PC (they are synched) and yet, my mail is still at 17.1 mb. I have therefore purchased more storage until I can figure out where I am going wrong. Where is all the mail that is taking up this vast amount of space ?