Extending outlook Add-in, Please suggest me

[Navalika]

I have one Add-in (Siebel), thru which I get 1 toolbar and also some Siebel
links. This add in only developed to work with contacts, Tasks and Calendar
but I need same toolbar when I open new mail and it should work.

My question is:
Should I use VBA for extending that add in or should I use COM
interoperability thru .net. Please suggest me.

Points:
*) I don’t have that add-in source code
*) That Add in is given by Siebel

 

[Ken Slovak - [MVP - Outlook]]

You cannot extend an addin written by another party where you don't have the
source code. You'd have to start from scratch with your own addin to add
whatever functionality you want and you'd somehow have to make it integrate
with Siebel if that's even possible.