Checking to see how much space you have left in your email

Under the "All Mail Folders" window pane on the left hand side, right-click and choose PROPERTIES at the bottom of the menu.

Choose the Folder Size button like below. This will bring up a box you can scroll up and down with. You will be able to see how much total space you have already used in each folder such as Inbox, Sent Items and Deleted Item. The TOTAL size should be under 100,000 KB. If you are over this size limit, find the folders with the largest size, close the below dialogue box  and begin deleting items or create personal folders to create more space.