Email delivery speed is not always the most important thing, but sometimes, it can be and for transactional email there’s an expectation from the sender and the user that messages will arrive almost instantaneously.
Using the correct number of IP addresses to match your requirements is what’s important and putting a strategy in place for delivering email is something every serious email marketer needs to do.
So how many IP addresses do you need?
It would be great if we could take inspiration from the answer to the ultimate question of life and say 42, but it’s not that simple – typically, things never are!
The first thing to understand here is the difference between shared and dedicated IP addresses because the right number of IP addresses really only applies when using dedicated.
Email marketers using shared IP addresses are at the mercy of things out of their control which can make the number of IP addresses completely irrelevant.
Generally, we’d say that if you expect to send 150k to 200k emails per day then you’d need 1 IP address. This will usually result in timely delivery of emails and ticks the box for most senders at that level.
Unfortunately, the number of IP addresses needed to retain that level of performance doesn’t scale equally as the number of emails per campaign increases.
As the number of recipients grows it’s more a case of looking at things like domain density and specific mail server rules to enable efficient high-volume delivery of emails to each domain.
We have clients that send 2 million+ emails within a single campaign and use only 1 or 2 IP addresses. Those extreme examples aren’t the norm and a more common approach is to have 1 IP address per 500k emails e.g. If you’re sending to 2.5 million people within one campaign then use 5 IP addresses.
Some basic assumptions
To help keep this post to a reasonably short summary there’s an expectation that you have at least all of the following in place…
- You’re not ‘sharing’ sending or click tracking domains
- Email authentication is in place (DKIM & SPF)
- Domains & IP addresses have been warmed-up
- Lists are clean and unresponsive users are removed regularly
- Your campaigns get good engagement rates
- Complaint rates are low
- Email content is good
- You’re using responsive email design (has nothing to do with email delivery but you should be!)
Too many IPs can lead to inadvertent “Snowshoe Spamming”
Use too many IP addresses and it looks very suspicious. There’s no need to spread legitimate email campaigns over lots of IP addresses.
“Showshoe” refers to the Spamhaus definition…
“Like a snowshoe spreads the load of a traveler across a wide area of snow, snowshoe spamming is a technique used by spammers to spread spam output across many IPs and domains, in order to dilute reputation metrics and evade filters.”
You can read more info about this on the Spamhaus website here.
Delivery speed doesn’t necessarily increase when you add more IP addresses
This is a frequently discussed topic with our agencies and the thing to remember is there are many influencing factors when it comes to how quickly emails are delivered.
To find out more, take a look at this post about how fast Instiller can deliver emails.
Our advice is to take a sensible approach
Try not to think more IP addresses will make things better. More IP addresses for growing volume is a good strategy but it’s not the full picture.
First focus on ensuring all of the best practice elements of setting up sending and click tracking domains are in place, plus your lists, content and data management are all spot on.
When that’s done, be realistic about the frequency of campaigns and the number of emails you’re actually going to be sending.
That’s a good base for being able to choose the correct number of IP addresses and we find that it makes it much easier for us to give solid advice to our agencies so they can meet the demands of their clients.