It looks like your account is growing really fast.
Outlook.com storage is designed to grow at a rate that serves the needs of the vast majority of our customers. Once in a while, a customer's storage needs grow faster than expected. We've provisioned additional storage for your account, but you might want to delete some of your old mail.
Here are a few suggestions to help you manage your account:
Sweep your inbox clean. You can delete all messages from unwanted senders in a few clicks. Learn how.
Let Outlook.com manage your Newsletters. Schedule automatic cleanups with Sweep so you only keep the latest deals or newsletters. Learn how.
Make the rules work for you. You can set up your Outlook.com account to automatically delete unwanted email. Click Options, click More Options, and then click Rules for Sorting New Messages.
Unsubscribe or mark unwanted mail as Junk. You can find Unsubscribe links within some of the Newsletters you receive. If you can't find them, mark the mail as Junk and Outlook.com will begin filtering such mails to the Junk Folder.
Create an Archive on your Hard Drive. Set up a folder on your PC hard drive where you can save large attachments. Then delete them from your inbox.
Store your data on SkyDrive. Save large attachments to SkyDrive, then delete them from your inbox. Learn about SkyDrive.
Sincerely,
The Outlook.com Team