Yes, Go to "Client" and "Send Email", you can send to all clients and resellers or you can go to "Client" area, "Edit Client Circle" and add a new circle. There you can select chosen clients/resellers and save, it will be available at the recipient dropdown on Send Email.
But this does not send mails to all mail accounts. only to the clients and resellers but not the mail accounts added by the clients
ah I am sorry, yes. Initially I got you and lost you on my way to check. It was very late =) Please excuse me. I do not see a way to achieve that without some extra programming. Code: SELECT email FROM `mail_user` WHERE ( disableimap = 'n' OR disablepop3 = 'n' ) AND access='y' executed in phpmyadmin may give you active email addresses. Though I may have missed a field but I think it is good enough if you check the recipients before sending. Does this help or not at all? Maybe later I could test something as a dirty hack for you but I just woke up so bear with me =)