You had me confused for a moment because Outlook is an email client. (i.e. a program totally separate to your web broswer, that can be used to handle email accounts). However I now see that you're referring to Outlook.com, which is a webmail service accessed via your browser. (Only Microsoft could be stupid enough to give two different things the same name; it leads to lots of confusion!).
I've been ploughing through five pages of this lot:
http://answers.microsoft.com/en-us/outlook_com/forum/osettings-oemailset/can-the-inbox-column-width-be-changed-on/6822e5fb-885e-4602-9527-a88cec542e01
If I've read it correctly (on page 3) the problem comes down to the fact that Microsoft have optimised the Outlook.com website for display on monitors that have a different resolution to the one which you're currently using. (That's Microsoft for you. Totally bloody useless!). So changing your screen resolution might be the best (or only) option for you.
Better still, simply switch to a
decent email service:
http://www.gmx.co.uk
(You can use the mail collector facility to get your Outlook.com mail forwarded to your new address).