how to maximize the attachment size deliverable in exchange 2007

We user Symantec Encryption 3.3.2 to host a Web Messenger site.

It delivers files to an Exchange 2007 server. I was using an Exchange 2003 server previously and that could accept attachments up to 15 MB per message.

Now clients can upload files in Web Messenger up to 15 MB but the server can only deliver files as large as 6 MB to exchange mailboxes. I think a setting in Exchange 2007 is limiting the file size it will accept.

I would appreciate someone pointing me to where that setting is in Exchange 2007 Management Console.

Thanks in advance.