[Dovecot] Postfix issue but I want to fix it here...

Hello, Dovecot bunch and Timo. I am using Sylpheed as my Dovecot/IMAP client. At home behind my LAN Sylpheed can send email because the Postfix SMTPd views my LAN as a trusted network. No such luck when I'm away from home. I know it has something to do with configuring the relay access elements but what I have tried so far does not work. I'm sure someone has had this simple issue previously. The error condition and other particulars follow:

OS: CentOS, Windows XP SMTPd: Postfix 2.3.3 IMAP: Dovecot 1.2 Mail client: Sylpheed 2.7.1

Error condition: Error occurred while sending the message: 554 5.7.1 messages-noreply@linkedin.com: Relay access denied