Yes.
You should send the appropriate MIME encoding headers for the encoding that you're using in your application.
You do KNOW what encoding you're using throughout your application, and are being entirely consistent throughout it (web input, output, database etc?), aren't you?
See the MIME spec or examples for exactly which headers you should set. If you're using a MIME library to create messages (e.g. with HTML or attachments), refer to its documentation too.
Mark