Aaaaaahhhhh, the killer question (literally if we're talking about your sender reputation). It's funny, because I don't think I've ever covered this topic here, even though it's a question that comes up regularly.
If I take the time to write an article on the subject, it's because I've been asked this question very regularly lately and just this morning in the context of a deliverability audit.
So the question was, "But why do you want us to lower the number of IPs we shoot with, when we've always been told that the more IPs we have, the more effective it is?"
Well, first of all, it is true that there was a time when shooting from many IPs allowed to be less fooled. This was true for example because the spam complaint thresholds before blocking at some ISPs were absolute volumes. Today, because of this practice, everyone has switched to %age thresholds. So it doesn't work anymore.
Then there may be some good reasons to have many IP addresses. In general, this reason is related to the speed of sending. When you are in the private sale sector for example, it is necessary that all the emails arrive in a very short time window (1/4 of an hour, half an hour, ...) and we all know that sending emails is not done "in real time".
The main reason why you should not exaggerate the number of IP addresses, is also related to the sampling that operators do and that will allow you to increase your reputation according to the behavior of your recipients. This problem can appear on two different occasions:
- Migration to a new router: In this case, if you have brand-new IPs, you'll need to warm-up them. In this case, webmails like Hotmail will deliver all your e-mails as spam and only let a few through, so that you can measure the reaction of your recipients. If the response is positive, your e-mails will gradually move to the inbox until the WarmUP is complete. If you send from too many IP addresses, the volume sent by each of them will be very low, and the number of samples going to the inbox may be close to zero. Your Warmup may last a long time.
- Getting back on track after deliverability problems: It's a bit the same scenario as for the previous point. One of the most effective methods when you have decided to change your deliverability practices is to start a warmup from scratch, with very low volumes but hyper responsive recipients. This allows you to rebuild your reputation, but also to know at what level of activity the recipients have a negative impact on your deliverability. The concern here is exactly the same. A too low volume will arrive entirely in spam, and the samples delivered to the inbox will not be sufficient to get back to a satisfactory performance.
Do you know Snowshoe spamming? It is an attack carried out by spammers and consists of sending a very large number of emails in a very short time to a very very large number of different IP addresses. Obviously you wouldn't want to be compared to such a practice 🙂
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Yes, but then, how many IPs do I need?
First of all, this is a method that I have been using for some time but which is not universally used. I don't claim to have the universal truth on the subject, so don't hesitate to give me your opinion on it.
The rule of thumb is to consider that an IP can swallow between 100,000 and 300,000 emails per hour (this is a range that can be wider, depending on your reputation and the number of destinations you address). If for you the speed of sending (I push the button and x minutes later my recipient should have received the email) is not paramount, I generally consider 250,000 as a good compromise.
So if you have 500,000 emails to send each day, with standard constraints, two IP addresses should be enough.
Where it gets a bit tricky is when your constraints are not standard, irregular frequencies, need to manage large peaks, ... there, you can try to work on your average emails sent each day versus the maximum volumes of your peaks. But if your averages are multiplied by more than 3 during your peaks, you'll have to ask yourself other questions, such as going back to shared IP, there, it's a case by case basis.
Don't forget to isolate your most risky/important emailing programs
Another essential point to consider is the separation of your different programs. I won't deal with this point in depth here, but when you separate a reactivation program, transactional emails and a marketing program, you obviously have to do this work separately, according to the parameters of these different programs.
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