It is a fault with the phone. I could only delete the mailboxes and then re-configure them to get rid of the problem. Unfortunately got the same problem with a voicemail but after trying all the fixes the icon and message notification could not be deleted and the phone is being replaced. Speak to yur provider and explain that it is a fault on the phone.
Thanks for the reply. I will keep an eye on it. I did manage to get rid of it (for now) . I delved deeper into my Hotmail account's folder's through the Hub drop down menu which lists all your accounts and expanded them. Its methodically went through each folder until I came across a folder (I think it was a spam folder) and found around the number close to what was attached to the icon and deleted them all. Rebooted and the icon disappeared. What was also curious was the icon associated with the files I deleted. They weren't mail icons, they were folder icons and I think they were yellow or an orange color. I would be interested to find out if your new one develops this issue again. Maybe in my case it was a corrupt sync or interruption with the network data flow during setup of my accounts.