Group rosters have an option to enable Online Messaging. This will allow all the members of the roster to send messages via the DASH Online Message Center.
Even when Online Messaging is turned off team managers can still send messages out to their players.
The teammates will only be able to reply directly to the team manager from the email itself, since the Message Center on DASH Online will be turned off for that team. To do so recipients can simply click 'reply' from the email account to respond directly to the team manager.