email bouncing back as the IP is dul


Were having a problem with email bounceing back when sent to several organisations stating our IP is dul, the exact message is...

      '' on 10/11/04 12:24
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            < #5.5.0 smtp;553-mail rejected because your IP is in DUL. See>

Now I'm no expert, so correct me if I'm wrong, from looking around it seems this error is usually down to the IP address being on a black list which companies subsribe to to cut down on spam. One problem is usually the response comes back with a company to contact, or even the IP address that is being blocked which the above doesn't.

The resolves to the IP address of our email/web hosting company and I would doubt that would be blocked, I've been in contact with them and they haven't been incredibly helpfull.
I've a sneaking suspicion this may be a problem with the setup in our exchange 2000, but not to sure where to start.

Any help much appreciated.

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ikm7176Sr. IT ManagerCommented:
DUL -Dynamic User List, see the details below

Your best option is to us your ISP's SMTP server as a smart host or contact your ISP to remove your IP from the DUL


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mbaldyAuthor Commented:

ISP had submitted our IP address to the DUL,


Cheers ikm7176
ikm7176Sr. IT ManagerCommented:
thats great !
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