Will there be an impact on delivery if a sender with a bad reputation is on the same network as my server with a good reputation?
It is a possibility that your neighbour could cause you some pains along the way
if they are not tended to by your ESP. In many cases it depends on who is doing
the blocking and the number of bad actors on the same network.
The good news – for most ISPs they will notice the difference and act only on bad IPs. That is where your revers DNS is important – to show the distinct nature/sender on each IP.
Does this mean then that a unique sending IP address given to me by my ESP is not necessarily as “safe” as we might otherwise think?
Yes this is true, but new systems are being developed by the leading ISPs and
ESPs to help distinguish one sending entity from another. Systems like Domain
Keys (or Domain Keys Identified Mail) are able to distinguish the “sender”
reputation and begin the movement from IP reputation to a domain based
The possibility of collateral damage bounces is greatly reduced on an isolated IP address, especially when compared to that of a shared IP address.
How do escalating blocking systems work?
Systems like UCE Protect are a good example of an escalating block pattern.
Level 1 – Contains single IP addresses Level 2 – Lists larger netblocks based on the number of listings in Level 1 (4 or more IPs in level 1 in the same network) with increasing size based on the total number of IPs listed. Level 3 – Lists Networks with a lot of level 1 or 2 listings, possible listing an ASN (Multiple networks) of an ISP/ESP. (more then 100 IPs listed in Level 1)
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