[Mailman-Users] ERROR: User unknown

[Jon Carnes]

> Nov 15 10:17:54 cerveza postfix/smtpd[13257]: reject: RCPT from
> localhost[127.0.0.1]: 550 <julianh at apc.edu.ph>: User unknown;
> from=<apc-staff-admin at apc.edu.ph> to=<julianh at apc.edu.ph>
>
> What do this mean?  Can you help me please? 

This means that the user does not exist on the mailserver.  Try sending a 
messaged directly to "julianh at apc.edu.ph" and see if you get a bounce.  
I'll wager you will - with the message 550.