Sending mails is to build relationship with the group. Also communication is like a nervous system in the body. Only with communication, things can happen better in any organization. As well said monitoring whether CSAs and PSAs getting mails or not is very important. To make sure, I always make sure following things in my mail:
1) Includes questions which are responsive in nature
2) Ask for acknowledging the mail at the end
3) Arouse a curiosity questions in the mail