Office 2003 and Office 2007 offer users the ability to connect to the Exchange Server at the office from remote means via the use of RPC over HTTP/(s). This functionality is configured from the Outlook Settings screens. Under the Microsoft Exchange Settings you will see your Microsoft Exchange Server name and your "username".

Click on More Settings
Under Security tab, ensure that the appropriate logon network security setting is selected. For some it may be Password Authentication (NTLM).
Under the Connection Tab, select the check box next to "Connect to Microsoft Exchange using HTTP"

Click on Exchange Proxy Settings

Where it says Use this URL to connect to my proxy server for Exchange, type in the URL you use for outlook web accesss. It might be "mail.companyname.com" or "webmail.companyname.com"

Once that is filled in, on the next area where it says "Only Connect to proxy servers that have this principal name in their certificate"
You must fill in msstd: prior to the webmail URL again. In example: msstd:webmail.companyname.com

Ensure that Basic Authentication is selected below all of that. Then click on Ok.
Click ok again.
Click on Next then Finish.

Ok, now that you have setup your RPC connection it is time to modify the registry on your computer.

Click on Start/Run and type in REGEDIT. (This step is to be done by a trained technician. Do not attempt this in the case you are not avid with registry management and willing to accept all negative happenings from your entries/deletions) DNS is NOT responsible for the following processes and their outcome if negative/unexpected.

1) Hit enter after typing in Regedit at the run prompt.
The following instructions are based on whether or not you are running Microsoft Office 2003 or 2007. Only create the following key as is specified by the version of outlook you are using.

Outlook 2003
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\RPC

Outlook 2007
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\RPC

Right-click RPC, point to New, and then click DWORD Value.

Type ConnectTimeout, and then press ENTER to name
the new value.

Double-click ConnectTimeout.

In the Value data box, type 000493e0, and the click OK.

Right-click RPC, point to New, and then click DWORD Value.

Type ConnectTimeoutLow, and then press ENTER to name the new value.

Double-click ConnectTimeoutLow.
In the Value data box, type 000493e0, and the click OK.

Right-click RPC, point to New, and then click DWORD Value.

Type RFRTimeout, and then press ENTER to name the new value.

Double-click RFRTimeout.
In the Value data box, type 000493e0, and the click OK.

Exit Registry Editor.

The above instructions were taken from a Microsoft Q Article. All rights reserved to Microsoft for this information.
The URL to the page where it exists is at: http://support.microsoft.com/kb/831060

On top of the above information also do the following.

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\RPC
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type DefConnectOpts, and then press ENTER.
5. Right-click DefConnectOpts, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. Exit Registry Editor.
8. Check the effect by using the NetBios name.

This will ensure that the system won't timeout while waiting for a response from the mail server.