email to web services

I am connected to several web services that will take email from me -- two are Twine and Multiply. In each case there is an email address that I use for sending the message.

I would like to send email messages via messagedance, but it looks like I can only send email to friends who have replied to an invitation. And the services are not set up to respond.

Am I misunderstanding something?

Is there a simple way to set up those email addresses so I can send to them?

Thanks