The Microsoft Forefront Server Security Support Blog points out that Spamhaus has recently phased out some of their RBLs.
It’s come to our attention recently that Spamhaus has phased out the old SBL-XBL list, which has now been replaced by the ZEN list (named after a guard dog).
If you’ve got Spamhaus configured in your Exchange connection filtering you will want to be sure you are not using one of the discontinued services. Short story is that sbl.spamhaus.org and xbl.spamhaus.org are no longer in service, and users should switch to zen.spamhaus.org. See the Spamhaus website for more details.
Actually sbl.spamhaus.org and xbl.spamhaus.org work just fine, we have no plans at all to phase them out (they’re 2 of our 3 major lists).
The only change was made a couple of years ago: zen.spamhaus.org can replace sbl-xbl.spamhaus.org since ZEN contains SBL and XBL and adds in the PBL list as well (so with ZEN you get the full Spamhaus set which works much better than SBL and XBL on their own).
However, although we encourage all users to switch from sbl-xbl.spamhaus.org to zen.spamhaus.org, we will not be phasing out sbl-xbl.spamhaus.org either since too many mail server appliances have it hard-coded.
Thanks for clarifying that.