How do I use my "Messages" to Email Someone?

I know I've done it in the past, but things seem to have changed. I can't figure out how to use Messages, if that's what I need to use, to email someone. In this case, I want to email a vendor about a product.
Comments
You can PM them, but not email them. If you go to your inbox and type their name in the recipient panel
OK, it's working. Thank you very much.