554 5.5.1 Error: no valid recipients

Hi,
We're trying to do away with our old domain and start using a new one. I've forwarded all the email from the old domain to the new one, everything has been working fine but now i seem to be getting this error.


Transcript of session follows.

Out: 220 mail.newdomain.com ESMTP Postfix (Ubuntu)
In: EHLO delivery.olddomain.com
Out: 250-mail.newdomain.com
Out: 250-PIPELINING
Out: 250-SIZE
Out: 250-VRFY
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-AUTH PLAIN LOGIN
Out: 250-AUTH=PLAIN LOGIN
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In: STARTTLS
Out: 220 2.0.0 Ready to start TLS
In: EHLO delivery.olddomain.com
Out: 250-mail.newdomain.com
Out: 250-PIPELINING
Out: 250-SIZE
Out: 250-VRFY
Out: 250-ETRN
Out: 250-AUTH PLAIN LOGIN
Out: 250-AUTH=PLAIN LOGIN
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In: MAIL FROM:<[email protected]> SIZE=9051
Out: 250 2.1.0 Ok
In: RCPT TO:<[email protected]>
Out: 451 4.3.5 Server configuration error
In: DATA
Out: 554 5.5.1 Error: no valid recipients
In: QUIT
Out: 221 2.0.0 Bye


For other details, see the local mail logfile

 

I used
https://www.howtoforge.com/perfect-server-ubuntu-12.10-apache2-bind-dovecot-ispconfig-3.
Its been working fine, it only started with the errors a few days ago

 

I cant seem to see any errors in mail.log but this only happens with this one domain. now emails are bouncing back

To: [email protected]
Subject: Mail delivery failed: returning message to sender
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
[email protected]
host mail.newdomain.com [xxx.xxx.xxx.xx]
SMTP error from remote mail server after RCPT
TO:<[email protected]>:
451 4.3.5 Server configuration error: retry timeout exceeded

 

yes and it is listed in /etc/postfix/main.cf

 

I changed the hostname and it seems to be working. thanks