I'm hoping someone can help me out. I've been banging my head against the wall for a few hours now. I'm a bit of a newbie, so please bear with me!

I have Zimbra Open Source Edition 6.0.8 32-bit on CentOS 5.5.

Let me preface by saying that Zimbra works great for me. I think it's because my network is static, and I have my IPs as a trusted MTA network.

My problem is that I have a user who is on a dynamic remote network from my Zimbra server. He's a home user, and his cable modem is DHCP. He can receive emails all day long from my server, but when he goes to send them, his messages are being dropped instantly from the server.

In Zimbra Admin > Global Settings > MTA; I have Enable Auth & TLS Auth Only enabled.

Here's what I'm seeing in the log files when I try and send an email.

Code:
Sep 14 22:08:25 mail postfix/smtpd[4378]: connect from DHCP.comcast.net[71.192.x.x]
Sep 14 22:08:26 mail postfix/smtpd[4378]: 0E9EB2379C0: client=DHCP.comcast.net[71.192.x.x]
Sep 14 22:08:26 mail postfix/cleanup[4393]: 0E9EB2379C0: message-id=<20100915020826.0E9EB2379C0@mail.MYSERVER.com>
Sep 14 22:08:26 mail postfix/qmgr[1330]: 0E9EB2379C0: from=, size=726, nrcpt=1 (queue active)
Sep 14 22:08:26 mail postfix/smtpd[4378]: disconnect from .comcast.net[71.192.x.x]
Sep 14 22:08:26 mail amavis[22980]: (22980-01) ESMTP::10024 /opt/zimbra/data/amavisd/tmp/amavis-20100914T220826-22980:  ->  SIZE=726 BODY=8BITMIME Received: from mail.MYSERVER.com ([127.0.0.1]) by localhost (mail.MYSERVER.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP for ; Tue, 14 Sep 2010 22:08:26 -0400 (EDT)
Sep 14 22:08:26 mail amavis[22980]: (22980-01) Checking: nS8lGTw53p6v [71.192.144.93]  -> 
Sep 14 22:08:26 mail clamd[9757]: SelfCheck: Database status OK.
Sep 14 22:08:29 mail amavis[22980]: (22980-01) Blocked SPAM, [71.192.x.x] [71.192.x.x]  -> , Message-ID: <20100915020826.0E9EB2379C0@mail.MYSERVER.com>, mail_id: nS8lGTw53p6v, Hits: 18.791, size: 726, 3306 ms
Sep 14 22:08:29 mail amavis[22980]: (22980-01) extra modules loaded: /opt/zimbra/zimbramon/lib/i386-linux-thread-multi/auto/Net/SSLeay/autosplit.ix, /opt/zimbra/zimbramon/lib/i386-linux-thread-multi/auto/Net/SSLeay/randomize.al, IO/Socket/SSL.pm, Net/LDAP/Extension.pm, Net/SSLeay.pm
Sep 14 22:08:29 mail postfix/smtp[4396]: 0E9EB2379C0: to=, relay=127.0.0.1[127.0.0.1]:10024, delay=3.5, delays=0.17/0.02/0.05/3.3, dsn=2.7.0, status=sent (250 2.7.0 Ok, discarded, id=22980-01 - SPAM)
Sep 14 22:08:29 mail postfix/qmgr[1330]: 0E9EB2379C0: removed
Earlier when we were trying, we'd get an undeliverable which shows the reason "554 5.7.1 : Relay Access Denied". But now all we see are those log file entries.

So, here's an overview of what I'm seeing:
  • Everything works fine for me. I am on an "MTA Trusted Network"
  • He is on an external network with a DHCP cable modem
  • He cannot send email to internal nor external email addresses.
  • If I put my known-working credentials in on his Outlook, I'm also getting the same error message above.
  • He can send email using the webmail function, so I know the MTA is working.


Can anyone help?

Thanks!