I have built a new Zimbra server .

Added in my domain and users. Receiving emails is no problem.

But sending to extrernal email addresses, even from webmail gives me something like :

Mar 22 03:03:39 z1 postfix/smtpd[2839]: NOQUEUE: reject: RCPT from myhost.mydomain.com[xxx.xxx.xxx.xxx]: 554 5.7.1 <someemailaddress@aol.com>: Relay access denied;

Can anyone help with this please?