Email Deliverability Test: A Detailed Look at the Best-Performing Tools

Latest Update: April 2022

Email deliverability can really make or break an email marketing campaign. Most marketers know the theory behind boosting email deliverability rates – maintaining clean lists, keeping subscribers engaged, building a good sender reputation, and so on. But many also know from experience that you can do everything by the book and still have your emails mysteriously disappear after being sent.

Based on our bi-annual email deliverability test, we’ve confirmed what many marketers have long suspected – different newsletter services do have different deliverability rates. And the differences, in some cases, are quite startling.

As a result, we’ve decided to share our results, and have committed to performing regular tests to make sure our results are always up to date. We’ll continue to add them to this page with each round of tests.

Because we believe email deliverability should be an important factor when deciding on which email tool is right for your business, we’ve also now added this as a criterion to each of our reviews.

Email Deliverability Test: Results Over Time

These rates represent an average derived from the five email deliverability tests in each testing round.

For an analysis of each of the individual test rounds, please follow these blog links:

Email deliverability test July 2017

Deliverability test March 2018

Email deliverability test January 2019

Email deliverability test July 2019

Email deliverability test February 2020

Email deliverability test September 2020

Email deliverability test March 2021

Email deliverability test October 2021

Email deliverability test April 2022

As you can see, email deliverability rates can fluctuate over time. Even providers that have done consistently well (ActiveCampaign and MailerLite) have seen surprising results in the past. There are also those that consistently perform pretty badly (Benchmark).

For an analysis of the most recent results, see the blog post (and infographic) from our latest round of email deliverability tests.

The average deliverability for all tools combined was 84.2% in our latest round of tests. That means 15.8% of all emails have either gone completely missing or have been caught by popular spam filters. Unfortunately, the average was slightly lower than the last round (85.3%).

This is slightly better than the results achieved through Return Path's research, which found that the average global inbox placement rate was 83%.

Where Exactly Are Emails Landing?

It’s no surprise that there’s a direct correlation between low email deliverability rates, and high rates of email flagged as spam. Below is a breakdown of where exactly emails ended up (whether it was the main inbox, a secondary tab, spam folder, or if the emails went missing), in each test round we’ve completed.

Inbox placement rates August 2017

Inbox placement rates March 2018

Inbox placement rates January 2019

Inbox placement rates July 2019

Inbox placement rates February 2020

Delivery rates September 2020

Delivery rates March 2021

Delivery rates October 2021

Delivery rates April 2022

Based on these results, we can start to see some general trends:

• Benchmark tends to have a higher proportion of emails get filtered to spam. On the other hand, the same emails sent through ActiveCampaign and Constant Contact were much less likely to be marked as spam
• Providers are finding it increasingly more difficult to land emails in the main inbox, as more are directed to promotional tabs

Email Deliverability Test: Rates by Internet Service Provider (ISP)

Thanks to the email deliverability testing tool Glockapps.com, we were able to see just how well each newsletter service performed in getting delivered to the four main ISPs – Gmail, Microsoft (Outlook and Hotmail), Yahoo and AOL. Based on our results, you can see that certain ISPs definitely look more favorably upon some tools than on others.

Please keep in mind that Glockapps sometimes adds or removes ISPs/a particular email client to reflect their current popularity on the market.

Deliverability to Gmail

Deliverability to Microsoft (Outlook and Hotmail)

Deliverability to Yahoo

Deliverability to AOL

What does this mean? Well, if you have a good sense of who your subscribers’ email providers are (in an ideal world for email marketers, that would be Yahoo!), you might consider choosing a newsletter service based on this. Of course, that’s often difficult to know. Plus, as our results show, deliverability to ISPs can change over time.

It’s perhaps more useful to just keep an eye out for any red flags. For example, Microsoft has, in the past, applied more stringent filtering to inbound emails, and some newsletter services – such as Benchmark – still struggle to get through.

Gmail Promotions Tab vs Primary Inbox

While the newsletter services were generally able to deliver to Gmail mailboxes just fine, not all ended up in the Primary tab. Nowadays, even emails that wouldn’t normally be considered ‘promotional’ are ending up in this folder.

Proportion of Gmail-delivered emails that ended up in Promotions tab

There’s no telling why some providers get sorted to Promotions and others don’t, as Google’s complex sorting algorithm is kept tightly under wraps. Ending up in Promotions is less than ideal, as your email is likely to get lost in the flood of emails that often make their way to that tab. Then again, if your email really is promotional and your subscribers are used to accessing emails from that tab, it may not be a problem. Furthermore, your email would be better off landing here than in the spam folder.

Our email deliverability test methodology

Our tests looked at some of the most widely-used email service providers:

• ActiveCampaign
• AWeber
• Benchmark
• Constant Contact
• ConvertKit
• Drip
• GetResponse
• MailChimp
• MailerLite
• Mailify
• Sendinblue
• Mailjet
• CleverReach
• HubSpot
• Moosend 
• Omnisend

Using Glockapps.com, we ran our first round of testing in August 2017. This round comprised of 5 separate tests conducted over several weeks. We wanted to make sure all conditions were equal, so in each test, we:

• Set up a sender subdomain for each of the tested tools
• Authenticated the SPF records and DKIM records where available
• Used the same email (always text-based, sometimes with links, and sometimes without)
• Sent to the same seed list of approximately 80 email addresses (representing 28 ISPs worldwide, including Gmail, Outlook, AOL and Yahoo; weighted according to the popularity of the email service)
• Sent all emails within a half-hour period

Over three thousand emails later, we finally had the results from our first testing round. And we found some pretty big differences in email deliverability rates between providers – ranging from 64 to 92 percent!

Happy with the comprehensive deliverability report we received from Glockapps, we repeated this very same test round in March 2018, and from July 2019 onwards, we included an HTML email as one of our tests. The latest email deliverability test we carried out was in Oct 2021 and we plan to conduct, on average, one every 6 months.

Why do some email marketing platforms perform so much better than others?

We’d love to know what the top performers' secret is – and we’re sure the other tools do too! What we do know is that the ISPs often have the last say on whether an email lands in an inbox. This means that they have to trust the mail server sending that email; in our case, that means the server used by the newsletter service.

If that same server also happens to be sending out emails for other clients that are considered ‘spammy’, the deliverability of your own emails could suffer. Newsletter services, therefore, make it a priority to maintain their server’s reputation. But some are clearly doing a better job of this than others.

Some email marketing services offer customers a dedicated IP address (rather than shared IP addresses), but these come at a high price, and are most likely not affordable for small businesses.

What does this mean for me?

With 50% of B2C users buying through marketing emails once a month, seeing your emails go undelivered could be costing you more than you thought.

When choosing a newsletter service, there are obviously many factors to consider – price, features, usability, and so on. But with these results, we’ve hopefully made it easy for you to shortlist (or discard) a few based on potential email deliverability rates.

Note that we said ‘potential’ – there’s simply no way of knowing for sure how deliverability will play out for each business. Our test results can give you a general idea of what you can expect, and what things to look out for, but your own experience may be very different. If so, we’d certainly like to hear about it!

How to improve email deliverability

In spite of our best efforts to establish the same testing conditions for each tool, it’s true that other factors can play an important role. As the sender, you have a responsibility to do your best to increase email deliverability by authenticating emails using SPF and DKIM and following best practice guidelines for creating and sending emails. Here are a few other pointers to bear in mind:

Email Verification

For the sake of their deliverability, no email marketer wants their emails bouncing.

There are tools to validate that an email address exists and can receive emails, which can help to avoid bounces and protect your sender reputation.

However, you can keep on top of list hygiene even without an email checker by unsubscribing inactive emails from your list. Some email marketing tools are stricter than others and will remove inactive emails from your list for you if they bounce a certain number of times.

Content

Try to only send marketing emails people actually want to receive, i.e. only send to fully opted in lists. Sending emails to non-permission-based lists will result in low open rates, high unsubscribe rates, and high spam complaints, all of which indicate an unsuccessful email.

These kinds of results can have a negative effect on sender reputation and will impact future deliverability.

Frequency

Find the right balance between sending too many and too few marketing emails to your subscribers. Remember that people are bombarded with tons of emails on a daily basis, so, in order to avoid inbox fatigue, only send what’s necessary.

You can even ask them to set the frequency at which they’d like to receive emails from you in their preferences. This can avoid spam complaints.

Monitoring activity

It’s not a good idea to have inactive people on your list as, if you’re sending emails to them regularly, this can affect sender reputation and impact deliverability.

Make sure to regularly check in with the less active people and give them the opportunity to re-engage or opt-out of future emails.

Check out these mass email service providers that help businesses send mass emails via SMTP protocol or API.