mail from a form

[cnocera]

The web site for domain yyy.com is on an ispconfig server (centOS). The domain email accounts are on another server. Mail from a form (PHP) will not be delivered to this domain (yyy.com) but will be delivered to all other addresses. The log entry is:
<xxx@yyy.com>: Recipient address rejected: User unknown in local recipient table
I set the domain to use an External Mail Server but it still does not send the messages. I don't think that I can put the same address on this server since it exists on the other.

Is there a way for mail addressed to xxx@yyy.com to be delivered?

[falko]

Did you select "External Mail Server" for the Co-Domains as well? Please keep in mind that yyy.com and www.yyy.com are two totally different things (technically spoken).

[cnocera]

Yes, I set External Mail server for the domain and co-domains.

[falko]

Are www.yyy.com and yyy.com still listed in /etc/postfix/local-host-names?
Any errors in your mail log?

[cnocera]

Falko, thank you.

Removing the domain from the etc/postfix/local-host-names file allowed the mail to get through.

But when any change is made on the ispconfig control panel, the domain is re-written to the file. Is there a way to not allow this single domain to be re-written?

[falko]

And you are absolutely sure that you've set www.yyy.com and yyy.com to "External Mailserver" in ISPConfig?