How many IP addresses do I need to send emails?

I often get asked, how many IP addresses do I need to successfully inbox. There is no one-size-fits-all approach, unfortunately.

PowerMTA is brilliant when it comes to handling multiple IP addresses for your sending needs. I have seen PowerMTA setups and configs where the client used over 200 IP’s in order to relay 100-150k emails a day. His inbox rates where shocking. Let me explain why more sometimes is less.

Using too many IP’s can be a risk and have a negative impact on your reputation. Using multiple IP’s for the wrong reasons, may raise a red flag with ISP’s, resulting in your email landing in the clients Junk folder, or to be filtered out completely.

• Snowshoe Spamming – is a spamming technique where a wide range of IP addresses are used to spread out the spam send rate and or load. Using a wide range of IP addresses makes it difficult for ISP’s to successfully identify the spam resulting in some of the spam to slip through.
• Waterfalling – is when multiple ESP’s are being used to send email. In this case, each ESP is using it’s own block of IP addresses. Spammers use one ESP to clean their lists, also called scrubbing, and another to send the actual marketing email. This technique is used by spammers and gray mailers.
• IP hopping – is simply using one set of IP addresses today, and next week you use new ones. ISP’s might throw you into the category of Snowshoeing or Waterfalling. If for some reason you have to change your IP’s, make sure they get warmed up properly, by relaying only a few mails per day through them. It takes a very long time to build a proper reputation for IP’s.

So how many IP addresses are right for me you ask. Good question 😉

I have seen clients send 2-3 million emails a day using 1 IP addresses with a successful inbox rate. The important factor here is, how quick do you need your emails to be delivered? If you need to inbox 5 million emails within an hour, you sure going to need more than 1 or 2 IP addresses and the correct software and infrastructure. In order to determine how many IP’s you need is actually very simple. You need to monitor your sending logs and reputation. ISP’s will throttle your email based on your sending reputation. Going through your logs will also give you some insight, why and who is throttling you. You may also want to have a look at the IPS’s postmaster pages. They are normally a good start to see and understand how many emails you can relay.

I also recommend using different IP addresses for different mail flavours. I.e

• Marketing messages
• Transactional messages
• Newsletters
• Old or in-active lists

There are positive and negative reasons for using multiple IP addresses when it comes email delivery. This all solely depends on you’re needs and situation. I hope some of the above will help you determine how many IP’s you should use.