I've looked at the headers, and its essentially the same issue as all the other BCC problems that everyone has - your mail server is not adding the appropriate headers needed to figure out who mail is delivered. You need to change your sendmail configuration to add in the appropriate header to the email so that Gossamer Mail's incoming.pl knows who the mail is being delivered to.

The reason that some BCC emails do get through is because the email address is added to the Recieved header (as it went through several different mail servers).

Adrian