MPP and Beyond

Lately we have seen an increase in ‘legitimate’ email being blocked by the extremely popular blacklist published by Spamhaus, zen.spamhaus.org. It is not that they are adding legitimate hosts to the block list, rather they have made a policy change in this list by adding the Policy Block List or PBL to the zen list. The policy block list will block IP addresses that should not be sending email based on published policies of email providers. For example, if you use Cox Cable in the US you are supposed to use their outgoing SMTP server. If for some reason you send email from your own SMTP server on their network then you will flagged by the PBL. One of our employees works in Eastern Europe and has an outgoing SMTP server on his cable modem connection and this is now flagged on the PBL. I am not saying that this is a bad thing, but it brings to light a few key points.

1) Be careful that you really understand the block policies of the RBL lists that you use.
2) It is not always appropriate to make reject decisions from a single block list unless you understand and agree with their policies.
3) If you don’t want the PBL included in your reject decisions and you otherwise trust the quality of spamhaus, which I have the absolute highest regard for, then use the sbl-xbl list of spamhaus as it does not include PBL.
4) If you use MPP you can enable MPP Custom Scoring to avoid making block decisions on a single RBL hit.

Technorati Tags: spamhaus, RBL, PBL, real-time black host lists, email security, mpp