Because the program code is contained within the form, it can be sent with an item to another user. VBScript programs are stored within a form.

While you use an add-in to extend form regions in a custom form, you can extend the functionality of form pages in custom forms by using VBScript. If, on the other hand, you want to write Visual Basic code that customizes how Outlook works (like a macro), use Visual Basic for Applications within Outlook.

If you expect your users to be using another application most of the time, and you want to give them the ability to send a message using Outlook or to access information stored by Outlook, write Visual Basic for Applications programs in that application that control Outlook through the Outlook object model. You use Visual Basic for Applications in one of two ways: Use Visual Basic for Applications in other applications (such as Microsoft Excel or Microsoft Word) to automate Outlook, or you can use Visual Basic for Applications within Outlook to control Outlook. One application of COM add-ins is to program form regions and create custom forms. You can create a DLL that can extend Outlook as a COM add-in.

You can also use other programming languages, such as C++, to control Outlook through its object model. If you want to create a separate application that accesses data stored by Outlook and uses Outlook to send and receive messages, use Visual Basic to create the application. In all cases, these programming languages control Outlook through its object model. VBScript is a simplified version of Visual Basic for Applications and is run within an Outlook item. Visual Basic for Applications is a subset of Visual Basic that is run within an application to extend its capabilities. Visual Basic is a full-featured programming language you can use to create stand-alone applications or dynamic-link libraries (DLLs) that extend other applications. Which you use depends on what you want your program to do. You can control Outlook by writing a macro in Visual Basic for Applications, a custom form in VBScript, and other languages that you can use to write an add-in, such as Visual Basic. Use Visual Basic to customize and extend Outlook.

Visual basic for outlook 2016