Since Outlook 2000 SP3 (optional) or Outlook XP respectively, some properties are blocked for security reasons, for instance the sender address of e-mails.
Since Outlook 2003 even blocked properties can be read in VBA without raising the security prompt by using the instrinsic Application object. That means, in VBA there's already a variable called Application, which should be used. You don't need to create this variable. And there's the rub, even with the official VBA help file: Examples often use the functions GetObject or CreateObject to retrieve a variable for the Application object.
The following examples demonstrate the difference. In order to test the examples, there must be at least one email stored in the inbox.
Example_1 shows how it does not work. Instead of simply using the intrinsic Application object, the variable olApp is set to the Application object by using the GetObject function. The effect is, the security prompt is raised as soon as you want to access the blocked SenderEmailAddress property.
Example_2 shows how to avoid the security alert: The variable olApp is directly set to the Application object without using the GetObject function.
In Outlook 2003 you should also pay attention to this: If you create a Run-a-Script rule, the rule wizzard will pass a blocked MailItem to your script. Since Outlook 2007 this doesn't happen any more.
In order to turn this blocked variable into a non-blocked one, you must apply the same principle: The variable must be derived from the intrinsic Application object.
Example_3 demonstrates how it does not work (Outlook 2003 only).
Example_4 shows how to derive the variable by using the instrinsic Application object. This way accessing the SenderEmailAddress is not blocked.