Maximum number of recipients in Mac OSX Server mail, outgoing (PostFix)

I posted this in the larger Q&A forum, but I realize it belongs here instead. I've set up Mac OS X Server on a PowerBook at my home (for my small company) to use strictly as a SMTP server. I bought a new copy of Mac OS X Server last week and installed it. I send about four pieces of mail each day to an opt-in list of roughly 1,800 newsletter recipients around the world. So the PostFix default for max recipients for outgoing mail is 1,000, I believe, because when I send mail it stops sending around that number of addresses (BCCed addresses). How do I change this parameter to 2,000 or 2,500 in PostFix? Simplest possible way, since I'm not a programmer. And the next question I have is how to set up Authenticated SMTP on the OS X Server. The instructions on Apple's Web site refer to a version that's older than my latest version of Server. Thanks, Jahan Salehi Greensboro, NC