Wrong server host name in mail header

[phoenix]

No, it's pointing on my public IP.

Well it should point to your LAN IP address.

The problem is not sending email, it's sending well header formated email.

Make the change above, restart the Zimbra server and post the headers you see when you send an email. Where are you sending this email to, is it an external account or an account on your Zimbra server?

BTW, what does the hostname on your server look like, whats' the output of the following:

su - zimbra
zmhostname

I assume that you have a valid domain name on your server?