Mail.dll requires multiple encodings to work.
By default in the Release mode, Xamarin applications link only most common encodings. Of course this is not enough to handle multi-national email messages.
If on startup your application receives MissingEncodingException error, you need to add MandroidI18n into your .csproj (e.g. App1.Android.csproj):
You might need to unload the project first to be able to edit it:
Alternatively you can go to:
Android project -> Properties -> Android Options
and select all possible encodings in:
Linker properties -> Additional supported encodings