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Best practices for IRP customers

Optimising Email Deliverability Using the IRP and SendGrid

This article describes the 'art' of email deliverability and provides immediately actionable advice to improve overall campaign performance, open rates and revenue.


Email delivery (the act of delivering email to mailbox providers), should not be confused with email deliverability.

Email deliverability, also known as inbox placement, is the ability to deliver email into subscribers' inboxes, as opposed to their spam folders. Maximising this is central to any complete email optimisation strategy.

The 'science' of both email delivery and email deliverability (for example, bulk email sending, correct SPF records, DKIM setup, email sending domains, IP pools, etc.) is fully taken care of by your SendGrid setup on the IRP platform. In fact, in recent weeks, by harnessing the power of the SendGrid API, we've been able to speed up our email delivery by more than x12 on the IRP.

This article therefore focuses on the 'art' of email deliverability and provides immediately actionable advice to improve overall campaign performance, open rates and revenue.

Subscriber engagement

Whilst avoiding spam traps and blacklists is obviously important, subscriber engagement is the primary contributor to a strong reputation and success in the art of email deliverability.

If your subscribers are engaging with your emails, then your IP addresses, domain and content all develop a good reputation and you will enter a virtuous circle of love, happiness and money! If your list doesn't engage, it will be seen as a poor indicator and you risk entering a vicious circle where your reputation starts to decline, more emails get flagged as spam and you get less and less engagement overall.

Therefore, the better you manage your lists, the more you monitor engagement and the more consideration you give to your subscribers' preferences, the better your reputation and email deliverability will be. This will result in a) happier subscribers and b) greater revenue.

So, now that we've established that subscriber engagement is key for email deliverability, let's see how we go about measuring and improving it.

How do you measure subscriber engagement and what are good benchmarks?

Measurable subscriber engagement metrics include: opens, clicks, unsubscribes and spam reports. Hard and soft bounces are not necessarily engagement metrics but they can also impact your reputation so you should also monitor these.

The core metrics to start with are opens and clicks:

  • As a broad guideline, acceptable email campaigns should have an open rate in the IRP of >10%. Below 10% is worrying, and anything lower than 2% will be extremely detrimental to your reputation.
  • Regarding clicks, over 4% is fine, 2-3% is worrying and anything under 1% is again a red flag for your reputation.

It's worth noting that we see open rates as high as 30% on the IRP – so don't let being above these minimum thresholds let you rest on your laurels.

Furthermore, the more granular you can be in your measurement the better. An overall decent open rate on a campaign might hide certain segments or elements of your list that are over/underperforming. Splitting your campaigns into segments allows you to measure better. You can also use SendGrid data such as 'Mailbox Provider Stats' to see if there is a particular mailbox provider that is returning below-par results.

Tactics to improve subscriber engagement

There are three core tactics you can employ to improve your subscriber engagement:

  1. Segment your campaigns.
  2. Manage your subscriber life cycle.
  3. Implement email content best practices.

These are discussed in more detail below.

1. Segment your campaigns using Mailing List Segments

Where time allows, you should be creating specific campaigns for specific user groups.

This may be as simple as creating a different email for different email profiles (for example, one for men and one for women) or for different demographic segments (for example, one email for UK/Ireland customers and one for the rest of the world).

Or you may want to plan campaigns for your highest-spending customers. They are after all the ones you want to keep loyal and get back to your site.

You might also want to add plans for specific campaigns to your calendar for specific customers when you know you will have a new relevant product launch or restock. This can be hard to manage if you don't have a marketing planner to structure this around, but with the correct preparation, it's just a matter of slotting these into the plan.

It goes without saying that the more you target specific user demographics, behaviours and tastes, the better they will engage with your campaigns. When you put this in the context of the overall detrimental effects of poor engagement on sender reputation, it becomes all the more important to work into your campaign planning.

2. Manage your subscriber life cycle

As with campaign segmentation by demographics or behaviour, the way you manage your subscriber life cycle has a direct impact on your subscriber engagement levels.

There are three stages to the subscriber life cycle:

Stage 1: Starting the relationship – set expectations
When starting the relationship you need to set clear expectations. Do this by customising the automatic Mailing List Signup IRP system email to ensure that when people sign up to your list they know what to expect. A well-written message here can set the tone for your new relationship, so make sure it's right. Remind users what they signed up to receive, what they can look forward to and how often they should expect to hear from you. You should never purchase lists or scrape email addresses, and only send to users who have explicitly opted in.

Stage 2: Building the relationship – engagement and conversion
When you're at your peak and you are building your relationship, make sure you look after your subscribers – provide them with the content you promised them, at the frequency you promised them. Do this with good planning and by monitoring engagement. Reduce the frequency of sends for subscribers who rarely engage. This not only will keep your subscribers happy, but it will indicate to the mailbox providers that you understand user preferences. If subscribers are disengaging, make sure you have automatic re-engagement campaigns set up in the background to entice them back in.

Stage 3: Ending the relationship – sunsetting policies
All good things come to an end. Recognising this is important. If a subscriber never engages with you, they are damaging your overall sender reputation and deliverability and they should be removed from your plans. The process of removing a user from your active mailing list is called 'sunsetting'. This is a critical part of maintaining and scaling an email program.

A sunsetting policy should be flexible – that means that the criteria for temporary list exclusion should be stricter when your engagement metrics are poor. This may be across the board or you may need to only implement stricter rules for particular mailbox providers where you spot deliverability issues.

As a very broad guideline, if a user has not engaged with an email in the last six months, we strongly advise against sending to them on a regular basis. This may of course be a shorter or longer timeframe depending on your product life cycle. The below quote from the anti-spam team at Hotmail rather reinforces this message:

“Sending to recipients who haven't engaged in six months is the kiss of death for your reputation.”
(Source: SendGrid)

The Mailing List Segments section of the IRP now allows you to make use of a 'Last Engaged' timestamp which tracks the last time a subscriber clicked or opened an email. The use of this criterion, in conjunction with other standard segment criteria will allow you to implement best practice sunsetting policies.

If you notice that you have particularly bad open rates with one mailbox provider, you can also make use of the new 'Mailbox Provider' criterion to apply stricter rules here. For example, if your open rates plummet at Gmail, add in a filter to your standard Mailing List Segments to exclude all Gmail recipients. Then set up a new segment that only includes Gmail addresses who have engaged in the last 30 days. Send to this segment separately. Maintain this strictness for a couple of weeks and monitor open rates on Gmail. As open rates improve, start to expand the criteria out to the standard settings again.

As a general rule, if mailbox providers see good activity, they'll reward it. If they see frequent emails to unengaged lists, they will punish it. If you're having deliverability issues with a specific provider, drastically cut back frequency and only send to highly-engaged users. Monitor results before slowly building up volume and frequency again.

Let's look at an example 'before and after' scenario to illustrate how you might initiate a simple sunsetting policy on your IRP:

Table 1. Before – sending practice without sunsetting policy

List / Profile / Segment Frequency Segment Criteria Content
Everyone 2 emails per week N/A News, promos, fashion ideas, etc.
Nike 1 email per quarter Purchased Brands = Nike New Nike in stock / Nike deals
Adidas 1 email per quarter Purchased Brands = Adidas New Adidas in stock / Adidas deals

Table 2. After – sending practice with sunsetting policy

List / Profile / Segment Frequency Segment Criteria Content
Everyone – Engaged Subscribers 2 emails per week Last Engaged With an Email < 180 days ago News, promos, fashion ideas, etc.
Everyone – Unengaged Subscribers 1 email per month or automatic re-engagement campaign Last Engaged With an Email > 180 days ago We haven't seen you in a while. Check out this amazing offer.
If you don't want to hear from us again, just click here to un-subscribe.
Nike 1 email per quarter Purchased Brands = Nike AND Last Engaged With an Email < 180 days ago New Nike in stock / Nike deals
Adidas 1 email per quarter Purchased Brands = Adidas AND Last Engaged With an Email < 180 days ago New Adidas in stock / Adidas deals

The above simple example would be considered a very basic sunsetting policy. This should be stricter if your deliverability is poor. Start here, and further enhance the policy as you get more comfortable with managing your segments.

3. Implement email content best practices

Using best practice content strategies breeds good subscriber engagement. We've listed some tips below to help you ensure that your subscribers engage:

  • Ensure your email content aligns with the expectations you set in your mailing list signup email.
  • Keep the main Call to Action (CTA) above the fold.
  • One or two main CTAs are ideal. Too many can decrease engagement.
  • Incorporate a nice mix between text and images. As a general guideline, images shouldn’t make up more than 40% of the message. Otherwise they will attract spam filters.
  • Ensure you place accurate 'Alt' texts on all images.
  • Keep total email size to under 100 KB. Ensure images are optimised.
  • Pay careful attention to the email subject and the first line of text in your email:
    • Three-word subject lines are optimal.
    • #hashtags perform poorly.
    • Emojis can work depending on your brand, but don't overdo it.

Note on the importance of subscriber engagement during a change in email delivery provider:
It's worth noting that whilst you should always be striving for optimal subscriber engagement, the most crucial time to do this is directly after you change email domain or sending configuration. When you change configuration (i.e. move to SendGrid) your reputation is not quite, but almost, starting from zero. This is why we strongly recommend 'ramp up' periods where you slowly build up the volume of your sends. The best way to do this is to segment your lists, provide relevant content and send to your most engaged users first. Please talk to your Account Manager for more guidance and information around this subject.


With the email delivery taken care of by the IRP and SendGrid, email marketing teams can focus on best practice list segmentation, subscriber life cycle management and email content planning to ensure optimal email deliverability. This will result in more emails being viewed, clicked and, ultimately, more revenue being generated.

Remember that poor performance doesn't just affect that one email campaign. It affects all future campaigns because it damages your reputation. Your actions and strategy will dictate whether you enter either a vicious or virtuous circle – so it's very important to choose correctly.


Anonymous - Useful contribution to knowledge
31 Mar 2023 12:26
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