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

Inka Wibowo

Latest Update: 7 Jan 2019

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 Deliverability %

Aug 2017

Deliverability %

Mar 2018

Deliverability %

Jan 2019

ActiveCampaign 85.8 96 97
AWeber 80.3 79.8 75.6
Benchmark 63.9 75.8 49.2
Constant Contact 89.74 93 90.4
ConvertKit 92.1 88 81
Drip 89.14 89.8 Not tested
GetResponse 87.5 78 80.6
MailChimp 87.52 82.6 81.6
MailerLite 77.6 89 92.6
Mailify Not tested Not tested 71.4
SendinBlue 83.9 75.6 77.4

As you can see, deliverability rates can fluctuate over time. There does however seem to be some consistency between those that perform the best, and those that perform the worst. Specifically, ActiveCampaign and Constant Contact tend to have the highest rates of deliverability, while Benchmark and SendinBlue tend to have the lowest. One to watch out for is MailerLite, who seem to be improving significantly every round. For an analysis of the most recent results, see the blog from our latest round of deliverability tests.

Across the board, average deliverability was 82.7%. This is consistent with Return Path's own 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 it went missing), in each test round we’ve completed.

Inbox placement rates August 2017

Inbox placement rates March 2018

Inbox placement rates January 2019

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

  • Benchmark, SendinBlue, AWeber 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
  • 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.

Deliverability to Gmail


Provider Deliverability % Aug 2017 Deliverability % Mar 2018 Deliverability % Jan 2019
ActiveCampaign 100 100 100
AWeber 100 100 100
Benchmark 50 100 0
Constant Contact 50 100 100
ConvertKit 100 100 100
Drip 100 100 Not tested
GetResponse 50 100 100
MailChimp 100 100 100
MailerLite 100 100 100
Mailify Not tested Not tested 80
SendinBlue 100 100 100

Deliverability to Microsoft (Outlook and Hotmail)


Provider Deliverability % Aug 2017 Deliverability % Mar 2018 Deliverability % Jan 2019
ActiveCampaign 50 100 100
AWeber 0 19 0
Benchmark 0 0 0
Constant Contact 84.4 100 100
ConvertKit 84.4 83 86
Drip 0 100 Not tested
GetResponse 50 11 20
MailChimp 50 40 62
MailerLite 0 100 100
Mailify Not tested Not tested 35
SendinBlue 50 13 0

Deliverability to Yahoo

Provider Deliverability % Aug 2017 Deliverability % Mar 2018 Deliverability % Jan 2019
ActiveCampaign 100 100 100
AWeber 100 100 100
Benchmark 100 100 100
Constant Contact 100 100 100
ConvertKit 100 100 97.5
Drip 100 100 Not tested
GetResponse 100 97.5 100
MailChimp 100 100 100
MailerLite 100 100 100
Mailify Not tested Not tested 80
SendinBlue 100 100 97.5

Deliverability to AOL

Provider Deliverability % Aug 2017 Deliverability % Mar 2018 Deliverability % Jan 2019
ActiveCampaign 7.1 100 100
AWeber 100 100 80
Benchmark 0 80 100
Constant Contact 92.9 100 100
ConvertKit 100 100 100
Drip 100 100 Not tested
Get Response 85.7 100 100
MailChimp 100 100 100
MailerLite 100 100 100
Mailify Not tested Not tested 74.3
SendinBlue 85.7 100 100

What does this mean? Well, if you have a good sense of who your subscribers’ email providers are (in an ideal world, 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 clearly apply more stringent filtering to inbound emails, and some newsletter services – such as Benchmark and AWeber – seem to really struggle to get through to their inboxes. So if your deliverability rates are inexplicably low, this may very well be the reason why.

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 – only 60% of MailChimp’s emails to Gmail ended up in Promotions (instead of 100%). Other previously-safe providers also had a much higher chance of landing in Promotions (MailerLite, SendinBlue, AWeber, ConvertKit). ActiveCampaign, GetResponse and Constant Contact were the only providers who ended up in Gmail’s main inbox each time.

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

Provider Aug 2017 % Mar 2018 % Jan 2019 %
ActiveCampaign 0 0 0
AWeber 0 0 60
Benchmark 20 0 0 (note – 100% went to spam)
Constant Contact 11.4 0 0
ConvertKit 0 0 60
Drip 0 0 Not tested
GetResponse 0 0 0
MailChimp 100 100 60
MailerLite 0 0 60
Mailify Not tested Not tested 40 (note – 20% went to spam)
SendinBlue 22.9 0 60

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.

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 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 per cent!

We repeated this very same test round in March 2018, and in January 2019.

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!

Does this mean marketers are completely powerless when it comes to the success of their campaigns? Not at all. If anything, these results really drive home the importance of understanding your subscribers – for example, how they engage with emails, and what content they’re likely to be interested in – and to tailor your email campaigns to their preferences. That way, even if you don’t have complete control over who gets your email, you’ll at least maximize their effectiveness with those who do.