You can reply by clicking the 'Go to conversation' button in your email and typing your reply from your PlanSocial conversation page. If the message is part of a group conversation, your reply will be sent by email to all participants, like a group email conversation. 

Your whole conversation will be visible in your PlanSocial conversation. (Do NOT reply to the email notification directly -- this is sent from a NoReply PlanSocial address.)