hide multiple recipients

Hi I'm new (to the list and php) - be gentle on me! I'm working on a script that will allow a client to send an email message to an email list that is pulled out of a database(mysql). I've got the script working sort of..., though it needs more work. Essentially, I pull the e-mails out of a database, put them all into one string, and then stick that string into the "to" field using php's mail() function. In the e-mail the recipient gets, all of the e-mail addresses are viewable in the "to:" field. Is there some way to hide those e-mail addresses? Many thanks in advance Jimbo