Sure, you could use conditional formatting the change the button.
1) Create a helper node in your form and call it ButtonPressed. This will be a boolean (yes/no) node.
2) Add rules to the button that sets the value of ButtonPressed to YES.
3) Add conditional formatting to the button that hides the button when the value of ButtonPressed == YES.
Some other thoughts on this could me to disable the button instead of hiding it, or creating another disabled button that reads "Please Switch to the Outlook Window" and display it when the original button is hidden.
Hope this helps, welcome to the fourm, and let us know how things turn out!
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Matt Faus
InfoPath Dev Texas
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge