The Group Email web part appears to be deployed just fine, but when you add the web part to a page, you are getting this error:
“Unable to add selected web part(s). Assemblies that implement ASP.NET Web Parts and are installed into a partially trusted location, such as the bin directory, must be compiled with the AllowPartiallyTrustedCallersAttribute set for import to succeed.”
When searching for the error details, it says that admin needs to add [assembly:AllowPartiallyTrustedCallers] to AssemblyInfo.cs.
You need to activate the web part in your site collection!
Activating a Bamboo Site Collection Feature