This article explains how to check the size of your email account in Outlook 2010.
Currently, all email accounts have a quota limit of 2 GB of storage on the email server. Follow the steps below to verify how much space your account is currently using when you are using Outlook 2010.
Since 1,000,000 KB = 1 GB, the above example displaying 683,462 KB converts to .68 GB, leaving nearly 1.5 GB of storage still available.
Be sure to look at the Server tab, not the Local tab. The size of your folders listed on Local do not count towards your email storage quota, since these files are being stored on your 'local' hard drive.