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

Inka Wibowo

Latest Update: February 2020

Email deliverability can really make or break an email marketing campaign. Most marketers know the theory behind boosting 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 email deliverability tests, 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 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.

Deliverability Rates Over Time

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

Provider  Aug 2017 %  Mar 2018 %  Jan 2019 % July   2019 % Feb   2020 %
ActiveCampaign 85.8 96 97 93.8 90.2
AWeber 80.3 79.8 75.6 80.4 85.4
Benchmark 63.9 75.8 49.2 41.8 45.2
Constant Contact 89.74 93 90.4 88 89.4
ConvertKit 92.1 88 81 91.4 60
Drip 89.14 89.8 Not tested 88.8 78.8
GetResponse 87.5 78 80.6 85.4 75.6
MailChimp 87.52 82.6 81.6 90.6 81.6
MailerLite 77.6 89 92.6 94.8 78.4
Sendinblue 83.9 75.6 77.4 88.8 95.4
Mailjet Not tested Not tested Not tested 84.8 94.6
CleverReach Not tested Not tested Not tested 79.6 80.8
Mailify Not tested Not tested 71.4 81.6 Not tested
Newsletter2Go Not tested Not tested Not tested 83 Not tested
Overall Average 83.75 84.76 79.68 83.80 79.6


As you can see, deliverability rates can fluctuate over time. There does however seem to be some consistency between those that perform the best (ActiveCampaign), and those that perform the worst (Benchmark). MailerLite and ConvertKit have, until recently, had pretty solid rates of deliverability – we're looking into why this happened in our latest round. For an analysis of the most recent results, see the blog from our latest round of deliverability tests.

Across the board, the average deliverability was 79.6% in our latest round of tests. That means 20.4% of all emails are either completely missing or caught by the spam filters – a significant jump from 16.3% last round.

This is not far from the results achieved through Return Path's research, which found that the average global inbox placement rate was 85%.

Where Exactly Are Emails Landing?

It’s no surprise that there’s a direct correlation between low 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

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

  • Benchmark and Mailify tend to have a higher proportion of emails that 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
  • The latest round saw a slight decrease in the percentage of emails the providers were able to land in the main inbox, with only 3 providers landing 80% or more there
  • Historically, MailChimp emails had a much higher chance of ending up in a secondary tab (instead of the main inbox), although this is changing. We explore this in more detail in the Google Primary Inbox vs Promotions Tab section below

Deliverability Rates by Internet Service Provider (ISP)

Thanks to 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 to reflect their current popularity on the market.

Deliverability to Gmail


Provider Aug 2017 % Mar 2018 % Jan 2019 % July 2019 % Feb 2020 %
ActiveCampaign 100 100 100 95 76
AWeber 100 100 100 83 81
Benchmark 50 100 0 13 34
Constant Contact 50 100 100 95 94
ConvertKit 100 100 100 95 80
Drip 100 100 Not tested 86.7 64
GetResponse 50 100 100 95 68
MailChimp 100 100 100 95 69
MailerLite 100 100 100 95 70
Sendinblue 100 100 100 95 93
Mailjet Not tested Not tested Not tested 95 91
CleverReach Not tested Not tested Not tested 89 82
Mailify Not tested Not tested 80 84 Not tested
Newsletter2Go Not tested Not tested Not tested 95 Not tested

Deliverability to Microsoft (Outlook and Hotmail)


Provider Aug 2017 % Mar 2018 % Jan 2019 % July 2019 % Feb 2020 %
ActiveCampaign 50 100 100 100 100
AWeber 0 18 0 56.9 60
Benchmark 0 0 0 33.8 23.1
Constant Contact 84.4 100 100 100 98.5
ConvertKit 84.4 69 75 95.4 0
Drip 0 100 Not tested 100 100
GetResponse 50 20 20 60 56.9
MailChimp 50 24 31 80 80
MailerLite 0 100 100 100 32.3
Sendinblue 50 7 0 78.5 98.5
Mailjet Not tested Not tested Not tested 43.1 100
CleverReach Not tested Not tested Not tested 100 63.1
Mailify Not tested Not tested 16 75.4 Not tested
Newsletter2Go Not tested Not tested Not tested 100 Not tested


Deliverability to Yahoo


Provider Aug 2017 % Mar 2018 % Jan 2019 % July 2019 % Feb 2020 %
ActiveCampaign 100 100 100 100 90
AWeber 100 100 100 100 100
Benchmark 100 100 100 20 7.5
Constant Contact 100 100 100 100 100
ConvertKit 100 100 97.5 100 97.5
Drip 100 100 Not tested 100 100
GetResponse 100 97.5 100 95 100
MailChimp 100 100 100 100 100
MailerLite 100 100 100 100 100
Sendinblue 100 100 97.5 100 82
Mailjet Not tested Not tested Not tested 100 100
CleverReach Not tested Not tested Not tested 100 87.5
Mailify Not tested Not tested 80 85 Not tested
Newsletter2Go Not tested Not tested Not tested 60 Not tested

Deliverability to AOL


Provider Aug 2017 % Mar 2018 % Jan 2019 % July 2019 % Feb 2020 %
ActiveCampaign 7.1 100 100 100 97.1
AWeber 100 100 80 100 100
Benchmark 0 80 100 20 0
Constant Contact 92.9 100 100 97.1 100
ConvertKit 100 100 100 100 97.1
Drip 100 100 Not tested 100 85.7
Get Response 85.7 100 100 94.3 100
MailChimp 100 100 100 100 100
MailerLite 100 100 100 100 100
Sendinblue 85.7 100 100 100 100
Mailjet Not tested Not tested Not tested 100 100
CleverReach Not tested Not tested Not tested 17.1 100
Mailify Not tested Not tested 74.3 62.7 Not tested
Newsletter2Go Not tested Not tested Not tested 57.1 Not tested

What does this mean? Well, if you have a good sense of who your subscribers’ email providers are (in an ideal world for email maketers, 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 have, in the past, applied more stringent filtering to inbound emails, and some newsletter services – such as Benchmark – still really struggle to get through. Though it has been slightly easier to get emails through to Microsoft more recently, your deliverability rates may still be suffering when sending to this ISP.

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. Perhaps this isn’t a surprise to anyone who’s used MailChimp, but our first two rounds of tests found that MailChimp had a much higher chance of getting relegated to a Promotions tab – even with emails that wouldn’t normally be considered ‘promotional’.

In the latest round, however, this changed – 0% of MailChimp’s emails to Gmail ended up in Promotions, however, they weren't delivered to Gmail's main inbox either – in fact, 31% were sent to Spam, or went missing altogether. Our latest tests showed that Constant Contact, ActiveCampaign and MailerLite had a much higher chance of landing in Promotions, though this wasn't the case in previous rounds. AWeber and CleverReach managed to stay out of the Promotions tab (though 19% went to spam).

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


Provider Aug 2017 % Mar 2018 % Jan 2019 % July 2019 % Feb  2020 %
ActiveCampaign 0 0 0 0 60
AWeber 0 0 60 18.7 (note – 17% went to spam) 0 (note – 19% went to spam)
Benchmark 20 0 0 (note – 100% went to spam) 6.7 (note – 87% went to spam) 20 (note – 66% went to spam)
Constant Contact 11.4 0 0 20 91.4
ConvertKit 0 0 60 20 34.3
Drip 0 0 Not tested 14.7 20 (note – 36% went to spam)
GetResponse 0 0 0 20 52.1 (note – 32% went to spam)
MailChimp 100 100 60 20 0 (note – 31% went to spam)
MailerLite 0 0 60 33.3 60 (note – 30% went to spam)
Sendinblue 22.9 0 60 0 12.9
Mailjet Not tested Not tested Not tested 40 42.9
CleverReach Not tested Not tested Not tested 14.7 0
Mailify Not tested Not tested 40 (note – 20% went to spam) 12 (note – 16% went to spam) Not tested
Newsletter2Go Not tested Not tested Not tested 54.7 Not tested

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, which is what has happened to many providers in the latest round.

Our email deliverability test methodology

Our tests looked at some of the most widely-used newsletter services:

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, plus SPF and DKIM records where available
  • Used the same email (always text-based, sometimes with links, and sometimes without)
  • Sent to the same seed list (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 deliverability rates between providers – ranging from 64 to 92 percent!

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 deliverability test we carried out was in February 2020 and we plan to conduct, on average, one every 6 months.

Why do some tools perform so much better than others?

We’d love to know what the top performers' secret is – and we’re sure some of 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’, 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.

What does this mean for me?

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 deliverability.

Note that we said ‘potential’ – there’s simply no way of knowing for sure how deliverability will play out for each business. Our 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 my own 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 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:


Try to only send 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.


Find the right balance between sending too many and too few 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.