When addressing an email to multiple recipients, the sSMTP butchers the headers when using the mail() function in mod_php. Although all members recieve the email, only the first recipient in the "To:", "Cc:" and "Bcc:" line are visible. NOTE: The first recipient in the "Bcc:" line is visible to all users. I fixed this by switching my MTA to exim.
It works fine for me net-mail/ssmtp-2.48 here.