Email bounceback/Listed on CBL

We are experiencing email issues at the moment which I think may be linked but have different error messages.

The bouceback error is:

            The mail protocol was unable to handle one or more requests because they were unrecognized or invalid. Please notify your system administrator.
            <riverexch.riverltd.co.uk #5.5.4 smtp;554 5.5.4 unblock

The domain linked to this error (who it's going to) is @lincolnshire.coop

We are currently listed on the CBL and I need to de-list our external IP address but wondered if the above is linked to this...as we're getting seperate bouncebacks that state it failed because we're blacklisted!

Urgent advice would be hugely appreciated.
smiffy07Asked:
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BlueComputeConnect With a Mentor Commented:
Unauthenticated relay is the same as 'open relay', it means that your mailserver is drastically misconfigured and will let anyone on the internet use it to send mail to anywhere they like.  This is unlikely to be the case, but better safe than sorry.  Run the MX Toolbox basic SMTP tests here: http://www.mxtoolbox.com/diagnostic.aspx
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BlueComputeCommented:
Looks like that NDR is caused by the same issue as your others - you've managed to get your IP listed on a RBL.

(SMTP Status Code 5.5.4 'transaction failed' and it refers to 'unblock', you seem to have cut the rest off?)

You'll need to head over to MX Toolbox and stick your IP in their blacklist checker.  Find out who's listing you as a spammer and why, then follow their instructions to request delisting.  You'll also need to fix the problem that got you listed in the first place - chances are that you're allowing unauthenticated relay, or you're subject to an authenticated relay attack using compromised credentials, or you have a mass mailer on your network etc.

While you do this you can get mail flowing by setting up a smarthost to handle your outbound mail.  I use dyn.com's standard SMTP relay service ('Mailhop').  Post details of your Exchange version and your IP address if you need more detailed advice.
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smiffy07Author Commented:
Thanks

I have de-listed our external IP and mail seems to be flowing again now. I am checking the AV and Malware software on our desktop PC's now. How do I check for unauthenticated relay??
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smiffy07Author Commented:
Thanks for the advice. I will run the SMTP test now.

I have been notified by several users that they are receiving Delivery Status Notification (Delay) messages from some external mail.

Any ideas what might be affecting this?
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