Your email quota is 25GB.
24.5GB - You will receive a daily warning that you are approaching your limit
24.75GB - You will be unable to send any email
25GB - You will be unable to receive any email
To find out how much of your quota that you are using:
In OWA, hover your cursor above your name in the left hand folder list. After a second a box will appear indicating your quota usage.
An example of the quota information is show below:

Your quota information can also be found in OWA options menu. Click on Options – See All Options.

The first screen that appears (My Account) will show Mailbox Usage.