server.domain.local #5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)>

This just started last week. On some of the emails the users send out, they get this message back. I've checked all the blacklists and they are not on any of them including the barracudacentral lookup. Can anyone shed some light on this for me?

There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <server.domain.local #5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)>

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Hypercat (Deb)Commented:
Is there any common thread among the emails that are rejected? For example, are they all to a specific external domain or group of domains? Coming from the same user or group of users internally? Are you seeing any error messages in the event logs of your Exchange server? If you have message tracking and/or SMTP logging turned on, have you checked to see if there are any errors showing up there?
Anything like that would help to identify what might be causing the problem.
Alan HardistyCo-OwnerCommented:
Have a read of my article about problems sending mail to one or more domains, but it does sound like a specific rejection, especially for you!
My article may highlight some configuration errors on your server / domain which need fixing before they like you again : ) 

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johnbowdenAuthor Commented:
I will turn logging on and get back to you. The messages are random failures but from one user, they are failing consistantly from two mail domains. So far, they have told me that they are the only two sites.
Hypercat (Deb)Commented:
Usually if the failures happen only to specific external domains, that indicates a problem either at the external email server or a router at that external site, or it may be caused by spam control software on the external domain. The fact that you're seeing a reference to a list of accepted hosts indicates that it might be a spam filtering rejection on the recipient's exchange server.
You don't have to be on a blacklist to be rejected as "spam" because the criteria that spam software and appliances are using to filter are getting more and more rigorous.  There are a couple of common causes of this:
  1. Your SMTP banner does not match the FQDN (public) of your Exchange server. By default, Exchange 2003 uses the internal host name of the server for the banner page, so if you haven't changed this, and assuming your internal and external host names are not the same, this might cause some servers to reject your email as spam. This setting is in the properties of the SMTP Default Virtual Server (ESM/Site/Servers/Protocols/SMTP) on the Advanced tab.
  2. Your Exchange server's public IP address does not have a PTR (rDNS) record pointing back to the FQDN of the Exchange server. This is another common cause of spam-related rejections. The PTR record normally resides in the DNS zone of the ISP that leases you your public IP addresses. Some ISP's will allow you to request that a specific PTR record be entered pointing to your host name, and some will only allow a generic PTR record.  The generic PTR record will work 90% of the time, but not always.

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