Old Caltype/Acucorp Query

Hello, we are using the older revision 1.21 CalType (c 20003). I understand that under Accounts Receivable there is an option to send the customer an email. However it doesn't send, instead brining up a blank grey window. I presume that there is an area to configure it, but I do not have access to manuals of that era of the program and searches thus far have been fruitless for internal readme files or general internet queries. Is there a user from that time period that could direct me where to configure the information required to send emails via this revision of CalType? Thank you for reading and responding.

Below is a visual reference of some menus.