When you want to adjust the Maximum Attachement Size in Exchange 2007, you can use this script to check where the size limits are set.

The only Message Size limit that is not set through Powershell, is the one for Outlook Web Access. This is done through the web.config file on the Client Access Server.

• First make a backup of the web.config file (default location c:\Program Files\Microsoft\ExchangeServer\ClientAccess\Owa).
• Open the file with Notepad
• Change the line <httpRuntime maxRequestLength=”30000″ />
  Where 30000 is the maximum message size (in kilobytes)
• Save the file (nothing else needs to be done)