Zimbra is up & running sending & recieving mail but I am getting occasional errors. My setup is Zimbra is behind a firewall and I have a DNS server supplying Postfix with the private IP of the server so it will deliver mail locally. The vast majority of the mail is going out but a few aren't making it.

1. Nov 2 16:47:39 mail postfix/smtp[25946]: 330FE4314F4: to=<stans@xyz.com>, relay=xyz.com[], delay=0, status=bounced (host xyz.com[] said: 550 5.7.1 Unable to relay for stans@xyz.com (in reply to RCPT TO command))
I had this problem with a couple of domains yesterday & turned off strict rfc821 envelopes and those domains will now accept mail. This is new today.

2.Nov 2 16:51:59 mail postfix/smtp[5987]: BD6944314F4: to=<ajohtyg@cfl.rr.com>, relay=none, delay=0, status=bounced (cfl.rr.com: Name or service not known)
I'm getting a few of these from different domains. This one won't resolve with ping but does show up in dig.
Any help would be appreciated