Is there any way to activate Mail App only for specific extension of attachments?

Question

I know there are activation rules to activate app if Item has an attachment. But how to check extension of that attachment? What if I want to activate only for .jpg files?

Answer 1

No, you unfortunately cannot.

This means that your app will show up on the bar if the email has any attachments. Then, inside the app's logic, you have to figure out if you want to simply say "this app is not supported on .jpg files."

See http://msdn.microsoft.com/en-us/library/office/dn148008(v=office.15).aspx for more details.