+PH/09 There is a new ACL condition "verify = not_blind". It checks that there
+ are no blind (bcc) recipients in the message. Every envelope recipient
+ must appear either in a To: header line or in a Cc: header line for this
+ condition to be true. Local parts are checked case-sensitively; domains
+ are checked case-insensitively. If Resent-To: or Resent-Cc: header lines
+ exist, they are also checked. This condition can be used only in a DATA
+ or non-SMTP ACL.
+
+ There are, of course, many legitimate messages that make use of blind
+ (bcc) recipients. This check should not be used on its own for blocking
+ messages.
+