Investigating Email: IP Addresses - It's Good to Share...Sometimes!

This article is written by Konstantinos Karagkounis, Deliverability Operations Lead at Emarsys and member of the Research Hub of the DMA Email Council .

A correct sending infrastructure is a crucial factor in email delivery and deliverability. The latest DMA’s Consumer & Marketer Email Tracker 2021, both sponsored by Validity, show a big misalignment between brands and consumers regarding the number of emails they believe they receive. This raises questions about the delta between the two figures (around 23%) and what happens to those emails. Spoiler alert - the DMA’s Email Benchmarking Report 2021 has registered a small year-on-year decline in delivery rates. A further reminder of the importance of making the correct sending setup decision.

Choosing between dedicated and shared IP addresses

One of the most frequent questions when setting up an email marketing platform is about sending infrastructure. The choice between whether to use shared or dedicated IP addresses is an important decision that the programme owner needs to address.

While there is no such a thing as a ‘one-size-fits all answer’, we have listed the pros and cons of both worlds.

Remember - if you’re not sure about which option you should go for, let the experts help you with your decision.

Before starting, let me specify a few definitions:

• Dedicated IP address: Used by a single sender and is not shared with others.
• Shared IP address: Used by several senders grouped together.
• Sender reputation: Like a credit score for email marketers, this metric is used by mailbox providers to determine email delivery (bounces) and deliverability (inbox placement). Usually, is calculated at domain, IP address and/or content level. Email senders can gauge their reputation using tools like Sender Score.

You should consider dedicated IP address(es) when:

• You are sending sufficient volume per day to build up and hold reputation
• You have an experienced team capable of managing the reputation of your sender domain and IP address(es), and want to isolate your reputation from other senders
• You have highly engaged lists
• You have a specific business case, where you need to use a dedicated IP address (e.g. advanced security in the banking sector)
• You want to take part in commercial certifications, which require the use of a dedicated IP address

What are the benefits of choosing dedicated IP address(es)?

• Establish and be accountable for one’s own IP address reputation; your emails will not get grouped with other less diligent senders and therefore you’ll have better inbox placement
• Easier to troubleshoot the root cause of deliverability issues; a dedicated IP address allows you to measure and interpret its performance
• Eligible for commercial certifications such as the one offered by Validity. You can find more information in the case study performed by Emarsys and Validity and see how your marketing programmes can benefit from it
• Sending over multiple dedicated IP addresses allows senders to segment based on message type, engagement level, etc.
• Eligible for ISP whitelists, where applicable
• Protects critical mail streams (e.g. transactional mail)
• It’s often aligned with mailbox providers’ recommended best practices – for example, Gmail says “send all messages from the same IP address”

However, it is not all about dedicated IP address(es)! Depending on the use case, you can find a powerful ally to assist your marketing programme in shared IP(s).

You should consider shared IP address(es) when:

• You need to onboard fast
• You send little and/or infrequent volume, which will not build up and hold reputation
• You may be a seasonal mailer, with activity concentrated in a few spikes across the year
• You do not have the internal resources to monitor your IP address reputation
• You are sending to low engagement lists

What are the benefits of choosing shared IP address(es)?

• These IP addresses are already established having sent high volume for years, and they hold a very stable cumulative reputation (the ‘wisdom of crowds’ principle)
• They are usually managed by the ESP for you - checking against any blocklists, monitoring for drops in sender reputation and other important delivery metrics
• Mail providers need specific and stable volume per day to hold the IP address reputation. With shared IP addresses this is achieved by design, meaning you don’t need to worry too much about sending consistency
• You will only need a short warm-up period for introducing your sending domain(s), and an IP address ramp-up is not needed. In other words, you can minimise the time needed to reach your full audience (days not weeks) while also ensuring smoother operations

If you are sending from a shared IP address pool, ask your ESP for more information about what type of clients you will be sharing the IP addresses with, and what the vetting process is when new senders are added. Also ask how the shared IP addresses are set up – for example, are there different pools based on different levels of engagement or sending practices?

As you will understand from the above, each case is different. Pros and cons should be evaluated, especially when you can choose which setup to use. Make sure you eliminate any preconceptions you might have, and do not leave this important choice to luck!