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📩How your ESP affects deliverability


New here? This is Inbox Hacking, a Free Newsletter for Awesome email marketers eager to boost Awesomeness. Email marketing insights, tools, & tactics sent twice per week. Someone forwarded you our Newsletter? Please join over 14,605 Email Marketers and sign up for your Free subscription. Today: A look at how deliverability is affected by your ESP choice + stats and facts to keep your emails from missing the inbox.

Hopefully, spring has sprung in your neck of the woods and if not, U-Haul is open 7 days a week. 

Inbox Hackers, I’ve got bad news. Your ESP could be the culprit that’s keeping your emails from landing safely in inboxes. Shocking news, I know. So if you’re looking at alternatives to your current email service platform or just starting with email marketing, this deliverability report breakdown will help guide those decisions.

Biggies in the Report 

The ESP deliverability report I came across was put out by Email Tool Tester (not sure what those folks do 😃).

But they’ve been holding ESPs’ feet to the fire since 2017. Testing their ability to land in inboxes.

What stood out to me (combined last 3 test avg.):

  1. The 800-pound gorilla’s struggles – MailChimp deliverability rate 87.9%
  2. Benchmark hit last place with a 43.4% deliverability rate
  3. HubSpot managed just 72.1% 

Even the most recognizable ESPs have flaws. So it may be time to A/B test→ another ESP entirely!

*We use Active Campaign BTW, which ranked #1 (93%) in deliverability during Email Tool Tester’s latest biannual test.

See? Email Deliverability Does Have a Ton of Moving Parts

It’s not just a cliche. 

Your email marketing can get derailed by any number of factors.

Can’t spend all your energy on subject lines. Or design options. Or segmenting until your mouse dies.

It takes a multi-pronged strategy. And who would think that your ESP would be unintentionally stabbing your deliverability in the back?

Let’s look closer at the crime scene.

The Long View on Testing Results

To show that any ESP can stumble, get this. Active Campaign saw a dip in September of 2020 with a 73% deliverability rate.

Active Campaign bounced back (no pun intended… ok, intended) in March of 2021 with a 91.1% showing.

The lesson? If you don’t track email metrics closely, a ton of your emails can end up missing, tossed in with spam, or hidden in the promotions tab.


It’s not smart to say “we’ll get ‘em in the inbox next month!” Pay attention to deliverability drop-offs to find the source and fix the issue.

ETT’s last 10 tests showed the following average deliverability rates for all tested ESPs:

2017— 83.7%

2018— 84.7%

2019— 79.7% / 83.8% (biannual tests)

2020— 79.6% / 85.2% (biannual tests)

2021— 88.9% / 85.3% (biannual tests)

2022— 84.2% 

Jan 2023— 80.9%🙈

Deeper View

This report also details various difficulties of ESPs delivery to specific mailboxes (i.e. Convert Kit struggled with Microsoft inboxing but was welcomed by AOL and Yahoo mailboxes).


Will you drive yourself nuts trying to figure out why one mailbox provider blocks your campaigns versus another? Yep, so meditate more or something, because deliverability details have to be addressed if you don’t want a ton of your emails to never see the light of day.

And don’t assume your ESP is successfully delivering the maximum number of emails simply because it’s one of the most-used email services or has bells and whistles galore.

🥇MailerLite had the best deliverability rate for the combined average of the last 5 testing rounds.

The Bottom Line on Deliverability and ESPs

Broad studies on deliverability can open your eyes to problems even though your subscriber base is unique. 

I preach on audience uniqueness a lot, right? But in this case, it doesn’t matter if you know your audience like the back of your hand if your ESP can’t get past Gmail’s spam filters. 


Or… even if your click rates are off the charts in Gmail, wouldn’t it be nice to get clicks from Yahoo users who have to dig just to find your emails?

Read on for fresh stats, Knowledge Base, & a bottom-line-boosting hack.

Knowledge Base

🔌Knowledge is power but first, little Zig Ziglars’ motivation.

Virtual events that don’t suck or cause cringe (a how-to).

📧Craft enhanced Welcome Emails to students.

Email A/B testing for dummies – or brainiacs clueless about A/B testing.

🔧AI may eliminate life on Earth but if you need to fine-tune an AI writer in the meantime…


Increase your open rates by up to 300%. Send emails when your subscribers enter their inbox, here’s how.

Spike your engagement and revenue with a new technology that enables you to know when your subscriber enters their inbox! How’s it work?

Step 1: Inbox Mailers identifies when your subscribers are checking their inbox🔍

Step 2: Inbox Mailers triggers your ESP to send an email while they’re checking it💥

This boosts opens, clicks, aaaand… sales!

Book Your Free Demo

Demo Inbox Mailers

Self Help 

You’d be shocked how much 5 or 6 words of encouragement mean.

That’s probably a lie, honestly. 

Hard to be shocked when you don’t witness the effects of your encouragement.

So you’ll just have to trust me— a little encouragement goes a long way. 

Don’t take my word for it, think back to when somebody encouraged you. 

They may’ve never seen the effects, but you sure as hell felt them.

*Shout-out to Inbox Hacking Subscribers → 

👷🏼‍♂️Devin at LA Fed (worker rights)

💡Balthazar at AlphaSights (knowledge on-demand)

Facts and Stats

  • A ‘no-reply’ sender address can appear as spam-like behavior even in transactional emails (Validity)
  • 19% of all emails have either gone completely missing or been caught by spam filters (Email Tool Tester) 
  • Worst-performing industries for inboxing success— Business Services, Telecoms, & Finance / Insurance (Validity)

Bonus: 88.21% of Email Marketers tip better than trust fund babies and NBAers.

From Our Sponsor

If you use email marketing for your business, you’re gonna want to check out Inbox Mailers.

They’re changing the game.

Here’s how…

Their software enables brands to know when subscribers are in their inbox while triggering an email that generates a 50% – 70% open rate→→ with no degradation in click-to-open rates.

The best part?

Inbox Mailers integrates with almost all major ESPs to easily and instantly fire your triggered email, using your ESP, from your domain at the time your subscriber is in their inbox.📩

>>>Book My Free Demo

Marketing Musings

It’s easy to overthink email marketing. 

Subject line night-sweats. Unsubscribe anxiety. Spam trap suspicions.

Sometimes, though, the simplest step can produce higher open rates.

Yahoo agrees with me (smart move 😁).

“Yahoo advises senders to avoid emailing at the top of the hour. Senders will generally encounter less traffic and reduced server loads if messages are spread out across a broader period.”

Rather give your elevator pitch in an elevator with 7 other marketers at noon or… just you and your potential client at 11:37 a.m.?

Get Hacking

Make a list and I don’t even care if you check ✅✅ it twice.

Write down options for A/B testing your email offers. Examples:

  • Free Shipping vs. 20% Off
  • Light vs. Aggressive CTA
  • BOGO vs. Double Reward Points
  • Referral Rewards (costs you $) vs. Referral Gamification (no cost to you)

Make the list today. You’ve got the rest of 2023 to test→ just two at a time.

*Know another brilliant email marketer? Please forward this newsletter to them (thank you).

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⚡Boost email engagement ASAP

🤖Using AI prompts for more efficient email A/B testing 

📝Please take survey below. Benefits residents of Okay, Oklahoma battling mediocrity.