Why do you need so many IP addresses (part 2)?
In my last post I discussed the background as to why an ISP will require their users to use their IP address allocation efficiently. I also mentioned in passing that I’d discussed ESP address allocation with both ESPs and ISPs recently.
The ESP was talking about assigning a couple of dozen IP addresses to each customer, because they might be useful for spreading load and it would provide some flexibility for moving from one IP address to another if one should get blocked. And IP addresses are pretty much free. They were wrong.
The ISP was considering an application for 750 IP addresses from a new ESP customer. They assumed that there was no possible reason other than snowshoe spam for an email related customer to need that many IP addresses. While I suspect they may have been right about the specific potential customer, the general assumption was wrong.
I’ve seen a lot of reasons given by ESPs for why they need so many IP addresses:
- I need at least one IP address per customer, to handle IP based reputation
- I need many IP addresses so my MTAs can handle the volume of mail sent
- I need many IP addresses so that I can work around ISP throttling limits
- I need multiple IP addresses per customer so that that customer can deliver mail in a timely manner
- I need multiple IP addresses per customer so as to manage filtering issues
- I need multiple IP addresses in different locations to provide redundancy against network outages
- I need multiple IP addresses in different locations so as to provide redundancy against blacklisting of my ISP
I’m planning on going through these in some future posts, pretty much like Godzilla goes through downtown Tokyo. Can you think of any I’ve missed? tell me in the comments!