Number four of seven in our occasional series on why ESPs need, or don’t need, lots of IP addresses to send mail properly.
I need multiple IP addresses per customer so that that customer can deliver mail in a timely manner
Why this is right
If your customer needs to deliver a message to 100,000 recipients within 30 minutes and 3% of them are at an ISP that only accepts 1000 emails per recipient per hour then you’re going to need at least 7 IP addresses dedicated to that delivery. See the previous post on throttling at ISPs.
Why this is wrong
Email is a store-and-forward protocol, more comparable to traditional postal mail than IM or SMS or fax. Delivery of the vast majority of a mailing list within thirty minutes is certainly possible, but relying on or obsessing about delivery of an entire list in that time period is unrealistic.
Why else this is wrong
A lot of spam is sent by botnets, networks of thousands of compromised machines that are used to send hundreds of thousands of copies of spam from a thousand different sources simultaneously. If you try and use a lot of source IP addresses to get a lot of copies of the same message delivered simultaneously then you’re likely to trigger anti-botnet measures. You need to have a history and a relationship with the receiving ISP to avoid that – and if you have that, you shouldn’t need multiple IP addresses.
Yet another reason this is wrong
Delivery of 100% of an email list in a timeframe measured in minutes is not something you’re ever going to be able to guarantee without heroic measures. If your customer is prepared to pay for those heroic measures, you still won’t be able to get to 100% but you should talk to a consultant who might be able to help you get to 99% in those rare cases where it’s something that the recipients might care about. If they’re not prepared to pay for those heroic measures, why are you wasting your time?