To send a "save the date" message you need one of our paid services which enable invites.
Click "messages" -> "invite" and uncheck the box ”show RSVP (ticket)/invite button”.
Now you can send an email where you can attach a calendar link which makes it possible to save the date in iCal or Google Calendar.
To follow it up you can schedule an email to be sent when the registration opens.
This you can do by clicking "messages” -> ”compose” -> ”send later” -> set time/date -> send message to ”invited”.