I have deleted ALL large mails from all the folders (Inbox, Sent) and I just have about 300 mails in my Inbox; however, under the folder section when I check, it shows the occupied space as 4GB, which is absolutely incomprehensible, as none of the 300 mails exceed 1 MB barely.

I have cleared ALL the other folders such as Spam, Trash.

How is this possible?