A big +1 to checking Spamhaus, specifically their DROP and EDROP lists. These two lists are what causes us most pain when acquiring IPv4 space as a lot of providers put auto blocking in place based on these two which can be difficult to get removed. I won’t even contemplate prefixes on either of these lists unless the seller knocks $5/IP off the purchase price because of the associated time and pain trying to clean it up. Sent from my iPhone
On Apr 3, 2019, at 11:49 AM, Valdis Klētnieks <valdis.kletnieks@vt.edu> wrote:
On Wed, 03 Apr 2019 15:20:17 -0000, "Torres, Matt via NANOG" said:
3. Check SORBS blacklisting. It should not show up except maybe the DUHL list(?). If it does, walk away.
SORBS isn't the only place to check. As an example, if Spamhaus doesn't have nice things to say about the block, it's time to start asking questions....
http://www.anti-abuse.org/multi-rbl-check/ has a fairly good list of places that could give your customer a bad time (whether or not the listing is deserved - the point is that being listed anywhere there will probably mean problems that have to be cleaned up)
You may all now begin the religious war over where else to check.