I am looking for a way to restrict MIME Types on files uploaded through a WFFM form. What I am really hoping for is a way to control the allowed MIME Types using the rules engine. Even if the solution doesn't use the rules engine, it may still help and is still welcome.
Update: We are using our own custom File Upload field that inherits from the OOTB one. I would prefer to not have to rewrite or modify this field for this solution to work, but I will if I absolutely must.
I am using Sitecore 8.1u2 and WFFM 8.1.160304 in an MVC solution.