Deliverability 101: Shared or Dedicated IP?

As children, most of us probably learned that it’s nice to share with others. It’s one of those timeless lessons that often carries throughout adulthood – but does it also apply to mail server IP addresses? It can, but there are a number of factors to consider to accurately make the determination whether a shared or dedicated IP environment is better for you.

The Basics

The question of shared vs. dedicated IP is most often asked when choosing an email service provider (ESP). While some ESPs specialize in one or the other, many offer both shared and dedicated IP options for senders depending on their sending patterns.

In a shared IP environment, one or more IP addresses are arranged into pools that are shared among multiple senders. At any given moment, mail from multiple senders is likely to be sending over one or all of the IPs in the shared pool. This also means any mail you send will be spread across some or all of the IPs in that pool.

A dedicated IP environment will provide you with an IP address that sends mail for only your organization. No other traffic from any other sender will use that mail server and it will be easily identifiable as ‘your’ IP.

Which Option is Right for You?

Hopefully we all have a clear understanding of what constitutes a shared vs. dedicated IP setup, but the burning question remains: which should you choose? There are a few factors that help make this determination:

  1. Sending volume.
    When you send from a dedicated IP, you need to be sure that you have enough sending volume to establish and maintain a reputation as a “known” sender at the ISPs you are attempting to reach. Volume recommendations will vary depending on list composition and other factors, but we typically suggest around 500,000 in average monthly volume as a good rule of thumb. This will help to ensure that getting a few extra complaints or bounces one day won’t completely derail your deliverability.
  2. Sending frequency.
    When considering a dedicated IP, the consistency of your send volume is every bit as important as the volume itself. In order to maintain that reputation with the ISPs, you need to send consistently and regularly. For example, if you send 1 million emails per month, but your sends are split 800,000 on the 3rd of the month and 200,000 on the 17th, you may not see the full benefits of a dedicated IP. We suggest at least 100,000 emails every week as a good starting point.
  3. Reputation.
    Even if you aren’t paying attention to reputation as a factor in your decision, you can bet your (potential) ESP is. If you are a sender who is following best-of-the-best practices, gets confirmed opt-in for every subscriber, and sends consistent high volume, you are not likely to see benefits from a shared IP pool. Since shared IP pools send mail for multiple marketers, the positive or negative reputation of each can impact delivery for every sender on the pool.

    While many ISPs are placing more weight on domain-based reputation, the IP address sending the mail is still a major factor at most every mailbox provider. As such, your mail delivery rate could be negatively impacted by the performance of others on the shared pool. Most ESPs have monitoring in place to ensure senders do not take actions that will seriously harm the shared IP reputation, but there will always be a higher level of shared risk than with a dedicated IP. However, by the same token, if you are not getting clear permission, sending irregular volume, or otherwise not following best practices, you are likely to see issues no matter which IP option you choose.

If you have the volume and/or consistency to support it, there are few cases where a dedicated IP setup would not be recommended. But if you are a smaller-volume sender, or only need to send sporadically, you can certainly find success on a shared IP pool with the right ESP.

– BG


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