How Shared and Dedicated IP Influence Email Deliverability

There are a multitude of factors that affect email deliverability. The content you send plays its part. The quality of a mailing list is important. Steering clear from spam traps and blacklists can never be underestimated.

One more thing that’s even more important than all of these combined is an impeccable reputation of the IP address you use for sending emails. Together with the quality of your domain, they form Email Sender Reputation – a key factor that’s used to determine whether an email should be allowed into an inbox, end up in a spam folder, or be discarded without a trace.

When it comes to your sending IP, you have two options – a shared or a dedicated IP address. Which one you should choose will depend on a lot of factors. Let’s explore the pros and cons of each approach.

Shared and dedicated IP – what are they?

Each email sent on the internet originates from an IP address (publicly represented by a domain). Each email sending provider (ESP) gives a set of IPs to its users and, using these addresses, distributes emails on their behalf.

Shared IP is a single email address that’s used by more than one sender. Frequently, there could be hundreds or thousands of senders using the very same address, especially on free email services such as Gmail. The performance and habits of each sender affect the performance of others in the same pool.

Dedicated IP is an address that can only be used by a single sender (domain). The entire history of such an address is built, usually from the ground up, by a company using such a service. ESPs offer a dedicated IP as an additional purchase or a plan.

Benefits of using a dedicated IP

Not sharing your IP with a bunch of anonymous senders sure sounds like a good idea. And rightly so – there are certain benefits of having a dedicated IP:

  • You’re responsible for your own fate. You’re building your own sending history from the ground up. If you’re doing it well, your delivery rates will likely reflect it.
  • You can more easily isolate any issues. When sending from a shared IP, it’s close to impossible to investigate any deliverability issues because of the sheer number of factors. When sending from a private IP, you can pinpoint specific issues and, if possible, address them quickly.
  • You can get whitelisted. As a sole sender from a specific IP, you can request for your address to be whitelisted with some ISPs, such as Yahoo!, AOL or MSN and services such as SenderScore or Goodmail. Being whitelisted gives a boost to your deliverability and can help with particular providers. These services typically don’t admit shared IPs.

Benefits of using a shared IP

Sharing IP with other email senders also has its benefits:

  • It’s more cost-effective. Without exception, sharing IP with other senders is cheaper than having a dedicated service. It can even be free with a low volume and select providers.
  • You can still enjoy a good reputation. If you choose a reputable ESP, it’s not like you’re going to sit on the same IP with hundreds of spammers and phishers and suffer because of them. ESPs do their fair share of the work to ensure that at least a decent quality of emails is sent from their IPs. They monitor hard bounces or complain rates and actively filter out those not meeting their standards
  • You benefit from the reputations of others. If you’re just getting started, send a low or inconsistent volume, you would have deliverability issues. But, because you’re sharing IP with more experienced senders, your cumulative volume looks far less suspicious from the outside. As a result, even if you’ve never sent emails with an ESP of your choice, you’ll probably enjoy very decent delivery rates.
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Shared vs. dedicated IP – which one should you choose?

You can probably already see that both solutions are targeted at slightly different groups of senders. Let’s reiterate anyway who should consider either of these approaches.

When to go with a dedicated IP

  • When you send a high volume (100,000+/month) on a regular basis. Sending such volume regularly will let you quickly establish a good reputation. You won’t have to look back at others and you won’t be clueless about what went wrong if numbers suddenly drop.
  • When you send a lot of corporate emails and need to get whitelisted. Many corporations require a sending IP to be whitelisted before a large volume of emails can be received from them. If this is the case for you, you don’t have much of a choice.
  • When you can afford the costs. A dedicated IP is far more expensive than a shared one. Often, you need to pay for setup along with a regular subscription. Prices vary.
  • When your shared IP is blacklisted and you can’t change the address. Sometimes, especially on free services, an entire IP can easily get blacklisted when a single email hits a spam trap. If you find your IP address on several blacklists, you may consider a move to a dedicated address. Just make sure the volume is there.
  • When you’re sure you’ve got a quality list. When sending from a dedicated IP, you’re much more vulnerable to spam reports, unsubscribes or low engagement. If you’re planning a move, clean your list first and make sure you only stick with the active subscribers.

When to go with a shared IP

  • When you don’t have a sufficient volume. If you’re not hitting at least 50-100k every month, you would be unable to build a good sender reputation. As a result, your emails would have a below-par performance, without much hope for improvement.
  • When you don’t stick to a consistent schedule. If you’re sending a big campaign every now and then and sit quietly for the rest of the time, such sudden spikes will look suspicious to ISPs. As a result, your emails may start bouncing out of nowhere. When you’re sending from the same IP as hundreds of others, these spikes are hardly noticeable anymore. ESPs also do their share of the work in gradually releasing large chunks of emails.
  • When money is a factor. If you’ve got better things to spend your money on, pick a good ESP and trust them to give you a good reputation in the package. Many ESPs offer very reasonable rates for their services. Need help picking a good transactional email provider?

Don’t forget to warm up your IP! 

If you decide to switch to a dedicated IP, make sure you incorporate a technique called IP warming. It’s about sending, gradually, more and more volume with a newly set up IP. This way, you teach incoming servers to trust your emails so that, by the time you’re ready to send that large marketing campaign, there won’t be any surprises. 

If you were to send tens of thousands of emails on day one, you would probably see a lot of unexpected bounces. Incoming servers would have no record of earlier activity and would take such a sudden increase in volume with a big grain of salt. And, if they did, this would affect the performance of your future campaigns. Disaster.

Luckily, many providers of transactional emails, such as SendGrid, Amazon SES or Sparkpost, now offer automated IP warmup that takes care of the process for you.

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