We experienced an issue this morning (10/08/2012) where any external user couldn’t send a mail to us and were receiving the following NDR.

“550 5.7.1 Recipient not authorized, your IP has been found on a block list”

Our setup is an Exchange Edge server with TMG installed.

From the event we pinned the issue down to a Real-time Block List and decided to see what our providers were.

Opened TMG console > Email Policy > IP Block List providers

We managed to pin down the issue to be DSBL (Which has been shut down since 2008 Confused smile) after removing this and appling the changes we were now receiving a different NDR which pointed to the Hub Transport Server was now blocking mail.


We now had to do the same change on the Hub Transport as we did on the Edge Server

Open EMC > Organizational Configuration > Hub Transport > Anti-Spam tab > IP Block List provider > Provider

then remove the DSBL provider.

After doing this all mail worked fine Smile


You may have slightly different set ups to us, so here’s the other way to remove DSBL from your block list providers.

Edge Server with no TMG

Exchange Management Console > IP Block List Providers > Providers and then Remove DSBL from there.