C# scripting is only supported in the Windows app
See the compatibility table
See also:
Using C# scripts to filter emails
Using C# scripts to parse emails
Using a C# script as an action
Overview of scripting in Email Parser
Download the Visual studio solution (SDK):
EmailParserScriptingSDK.zip
The file EmailParserScriptingSDK.zip contains a Visual Studio solution (a set of projects) where you can easily write and test your own C# code for custom filters, parsers or actions. It provides all the classes and calling conventions that a C# script in Email Parser needs. As Email Parser lacks debugging, autocomplete and other very useful features it is very convenient to develop your C# scripts this way.
Once the script is done and tested, moving the code to Email Parser is vey straighforward, just paste the contents of the class ScriptBasedEmailFilter, ScriptBasedField or ScriptBasedAction from Visual Studio to Email Parser.