Why not both? For the beginners always send an e-mail. Many beginners do not manage to SFI account and you will need to send them a message on their e-mail to make sure that they are going to read it. Later, when you get a better contact with your PSAs, you can agree to how you communicate via e-mail, SFI messaging, social networks, etc. Be sure to use team mailer for important information you want to forward to all your members.
