There was a SMTP communication problem with the recipient's email server #5.5.0 smtp;550 Client host rejected

I am running SBS Server 2003
Outlook 2003

While replaying to a message that I received I get this error message.
I can send/receive messages from other people and different domains, but some of them I am unable send to or receive.  I am pulling my hair over this one.  The server has been running fine for past 12 months, this problem happened recently in last 4 weeks.

The following recipient(s) could not be reached: on 2/11/2006 1:28 AM
  There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
  <server.ETCTransport.local #5.5.0 smtp;550 <[]>: Client host rejected: CABLE HS R#2>
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Chris StauntonCommented:
While some e-mail servers will still accept connections from ANYONE when sending mail.  Most are now cracking down on servers that don't match their name resolution and many other configuration problems.  My suggestion to you is this:  Change the setting in your Exchange server's fully qualified domain name.  To do this open your ESM (Exchange System Manager) drill down to your Virtual SMTP Server and right click on it and select properties, click on the delivery tab and then add your mail servers FQDN in the field provided.

Call you ISP and ask them to please create a PTR record for your IP with the name that you just put in FQDN.  This name should = what your MX record currently points to, so for you since I've looked at your record the FQDN and name you are reporting to your ISP will be

Next you should also create an SPF record to further help with mail delivery, you can learn more about SPF here

Hope this helps!



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mdrwiegaAuthor Commented:
Thank you for your replay,
Last week we have upgraded internet lines to 8MB, which changed IP.
After the upgrade it seems that the problem went away, at the same time people that try sending emails to our domain are getting this error.  This specific email was replay to one of our users.  We can send and receive emails, but some people are getting error messages.
There are no limits on the server and the user folder is around 25MB.
Any suggestions?

>From: System Administrator
>Sent: Tuesday, February 21, 2006 9:46 AM
>Subject: Undeliverable: RE: t e s t
>Your message did not reach some or all of the intended recipients.
>       Subject:      RE: t e s t
>       Sent:      2/21/2006 9:33 AM
>The following recipient(s) could not be reached:
> on 2/21/2006 9:46 AM
>             The message could not be delivered because the recipient's
>mailbox is full.
>             < #4.2.2>
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