What Is Email Marketing Deliverability and How To Improve It

What Is Email Marketing Deliverability and How To Improve It
27 September, 2021 • ... • 1481 views
Kate Shokurova
by Kate Shokurova

Email deliverability is one of the main email marketing metrics. Because every other effort is in vain if your perfect emails end up in spam folders. That’s a bummer! Let’s look at the top reasons why this happens and how you can improve your email deliverability rate.

But first, let’s sync our watches and agree on definitions.

Email delivery vs. email deliverability

There are two separate metrics: email delivery rate and email deliverability rate. Sounds similar but there’s a big difference.

Email delivery rate is how many messages were successfully received by recipients’ servers. Doesn’t matter if it’s inbox or spam folders. That is, we are talking about all the emails you sent minus those that bounced because of mailboxes being full or unavailable, not in use, not existing, etc.

Here’s a screenshot of one of Selzy’s own campaigns:

a screenshot
Out of 36,501 sent messages, 104 were undelivered. You can see what was the problem and if you click on any of them, you’ll see the specific addresses.

Email delivery rate is a rather technical thing and largely depends on your ESP of choice (email service provider like Selzy or Mailchimp). A good email delivery rate is above 99%. If yours is lower, that’s a reason to re-evaluate your ESP. Ours is 99.8% on average.

Email deliverability (inbox placement) rate is how many messages got to subscribers’ inboxes, i.e. all emails you sent minus bounces and emails marked as spam by recipients or their email services — Gmail, Outlook, Yahoo, etc. Each has its own set of anti-spam measures. You can only influence them by improving your sender’s reputation and making the content less spam-like.

That’s why email deliverability rate is a much more complicated metric than email delivery rate. It involves multiple factors and very much depends on the algorithms of specific email services. Your deliverability can be A-OK in Gmail and a total disaster in Yahoo. So unlike delivery rate, you won’t find any deliverability figures in ESP’s account. Still, there are some statistics for you to consider.

For their latest email deliverability benchmark report, Validity analyzed over 2 billion email messages sent in 2019, and here’s what they found:

Validity analyzed
The average email deliverability rate globally is 83%. 7% of emails went to spam and 10% were missing, i.e. blocked or not properly sent. Source: Validity

EmailToolTester has been exploring the subject of email marketing deliverability in different ESPs since 2017 and these are their latest findings to date:

According to this study, the average deliverability is 88.9% of inbox placement and 11.1% of emails missing or caught by the spam filters. Source: EmailToolTester

What affects email deliverability and why emails get to spam

Let’s look at the main factors that affect email deliverability. The thing is, 45% of global email traffic is spam (though this figure is way lower than before). To save us from it, email services use spam filters — algorithms that check billions of emails every day and base their “judgment” on certain aspects.

The quality of email lists

The first thing to pay attention to is the quality of your email lists. No chance for good deliverability if your subscriber base is full of non-existent and invalid addresses. To make (and keep) your email lists squeaky clean, read our article about email list cleaning.

But bounces are just for starters. The real problem begins when spam traps are involved.

Spam traps are email addresses that services like Gmail use to track unwanted traffic and identify its source. They can be of different varieties: sometimes email services create and leave them here and there on the internet for dishonest marketers to collect. Other times, they use real existing emails that haven’t been in use for some time.

It all can end up in a situation when you get reported as a spammer for sending to an address that was perfectly fine… a couple of years ago, but not anymore.

Kirill Kolpakovich
Kirill Kolpakovich

Head of Antispam · Selzy

What to do? We recommend you remove contacts that were inactive during the last 3 months or so. There are cases when you have to remove 24,000 inactive contacts from a base of 25,000. It hurts like hell, but you have to do it. Otherwise, you’ll get reported simply because some address has become a spam trap.


Authentication is a process when email services check the IP address of a sender for permission to send emails. For them, it’s like your ID that signifies that it’s really you and you’re of age to buy this bottle of beer. Without setting up authentication, you have no guarantees your emails will be delivered at all.

You might have heard about several things in connection with email authentication:

  • DKIM (DomainKeys Identified Mail) adds a digital signature to an email. Thanks to it, email services can check that it came from your domain.
  • SPF (Sender Policy Framework) is a TXT entry with a list of IP addresses (for example, Selzy’s) that a domain trusts to send emails on its behalf.
  • DMARC (Domain-based Message Authentication Reporting and Conformance) tells an email service what to do with a message next, depending on DKIM and SPF.

What authentication settings do you need? All of them!

Kirill Kolpakovich
Kirill Kolpakovich

Head of Antispam · Selzy

If you suspect that you have a deliverability issue or your emails end up in spam, it never hurts to set up email authentication. And even if there are no problems, set it up anyway.

I am often asked how to improve the deliverability, and sometimes I even forget to mention email authentication, because it is such a basic thing that any sender should have.


Sender reputation or sender score is your rating that email services calculate to determine whether it’s worth accepting emails from you. Algorithms for determining reputation are carefully hidden. Each service has its own way.

Reputation depends on:

  • Email regularity
  • How many emails are delivered
  • How many of them get read
  • Domain history
  • IP address history.
Kirill Kolpakovich
Kirill Kolpakovich

Head of Antispam · Selzy

A client comes to us, starts sending perfectly fine campaigns to a perfectly fine audience, but they go to spam. What gives? We start looking into things and it turns out that a client had previously used their domain to send spam, or bought a base, or something similar. So it turns out the domain has a certain reputation now and email services know about it. It’s easy to lose a good rep, but very hard to get it back.

Reputation is fluid. For each mailing, a sender gets or loses reputation points. To keep track of your reputation, popular services have special tools called postmasters. By registering there, you can track detailed statistics on email deliverability.

For example, this is how Gmail’s Postmaster Tools looks like:

Gmail’s Postmaster Tools
A rating of 65 is considered good.

The main indicators are IP Reputation (the reputation of the IP address used for mailing) and Domain Reputation (the reputation of the domain). There’s also SpamRate but it only shows the percentage of emails rated as spam by recipients.

The downside is that only those who send at least 200 emails per day to Google mailboxes can see the statistics.

Patterns and anomalies

Gmail, Outlook, and other email services also take into account the usual behavior of a particular sender and senders and recipients in general.

Patterns are the usual behavior of millions of other senders and recipients. So email services get suspicious if a user:

  • Marks several emails as spam at once. It happens when people give their addresses for lead magnets like books, discounts, freebies, etc., and are not interested in the next emails.
  • Doesn’t read emails or always deletes them right away. It means that they don’t find your emails interesting enough.

Anomalies are something that’s different from the usual behavior of a specific sender. For example:

  • Too many emails at once. If there’s a spike from 1 email per month to 5 a day, an email service thinks that something’s not right. What if you’ve been hacked?
  • Too many addresses on the lists in one go. Better not send to 1,000 people today and to 10,000 tomorrow.
  • Too many spam complaints at once. Email services know how many reports your campaigns usually get. So a sudden surge looks suspicious and may cause your next campaigns to go to spam also.
  • Sudden switch of the subject. You cannot just change the subject of your emails, people won’t be OK with it and you’ll a lot of complaints.

Content of emails

This includes everything that makes a message be what it is: layout, design, text.

Email services know the look and feel of spam emails, they analyze every aspect of your message and how people react to them and deduce whether they have something in common.

Low engagement? Looks like your emails are not relevant to subscribers and they would be better off not getting them.

Words and phrases like “Cheap” and “Once in a lifetime”? Sounds like spam.

Poor design and no mobile or web versions? Looks like you don’t pay enough attention.

Securelist’s spam reports

This is an example of last year’s spam emails taken from one of Securelist’s spam reports. Even in 2020, they still feature a lazy design that makes you think of the early 2000s. Spammers seldom bother to make their messages look good.

Legitimate brands make an extra effort to keep their emails relevant, clear, and technically optimized...

…while staying true to their brand. Source: Email Competitors

How to improve email deliverability

Time to go over specific tips for email deliverability improvement that come from the previous points:

Set up a clean email list

Make a habit of spring-cleaning (or whatever-period-cleaning) your email lists. The more inactive subscribers you have, the more unsolicited your emails look. If you’re moving to another ESP, always perform a thorough check of your subscriber base to cut the dead weight that pulls you down and tarnishes your reputation. Use checkers like ZeroBounce to run through the old database and remove broken and role addresses, and duplicates.

If a lot of your subscribers don’t open or click, run re-engagement campaigns and remove them if it doesn’t help.

Set up email authentication

Authentication provides a 99.8% guarantee that subscribers will get your emails. Without this initial step, there’s really no point in fussing about the content of your emails and other stuff.

To set up authentication, in Selzy, you need to go to your account and choose Settings:


Then Domain authentication:

Domain authentication

There you add the domain you use to send your campaigns from and get two records that you need to copy to your hosting account. It usually takes a couple of minutes and up to a couple of days for the hosting to confirm it. That’s it, you’re ready to go!

Start your mailing by warming up the base and domain

Remember the part about patterns and anomalies? Email services like it when things are smooth and gradual. That’s why there’s such a thing as IP and domain warming in email marketing. When you’re starting with a new ESP and with email marketing in general, warm up the base first. Otherwise, what should an email service think if your list has suddenly increased 2-3 times in one day? You probably bought a base or were hacked.

Take a small part of addresses (about 200-300), send a campaign, and increase your mailing volume every day.

Provide simple subscribe and unsubscribe options

The best subscription practices are:

  • Making the process memorable for a person to get a definite and clear idea that they have indeed subscribed to your newsletter
  • Informing them of what they are going to get: state the subject of your emails and their frequency and stick to it
Really Good Emails

A pop-up subscription form on Really Good Emails. They describe what they are going to send and how often and offer to check the box and press the button.  

As for unsubscription, then:

  • Don’t hide the unsubscribe button, it will only make things worse. When people can’t find it, they choose the one called Report spam instead.
  • Make the unsubscription process easy and one step, don’t make a person do extra manipulations after they’ve already clicked on Unsubscribe.
  • Send a confirmation note saying that you’re sorry and you hope to see them again. Offer to choose the reason for unsubscription and an opportunity to resubscribe in case they made a mistake.
Kirill Kolpakovich
Kirill Kolpakovich

Head of Antispam · Selzy

Don’t ever hide the unsubscribe button. It should be visible and it’s better when it’s in the footer as well as at the beginning of an email. It’s much better if a person unsubscribes this way than sends a report because unsubscriptions don’t affect your reputation. Unlike spam complaints.

Make sure your emails are in line with the law

Needless to say, for better deliverability and fewer spam complaints, make sure your base is legitimate and every one of your subscribers gave their consent.

  • Include an “I’m OK with receiving emails from you” checkbox to your subscription forms. By putting this box, you make sure your audience is more committed and you are better protected by laws.
  • Use double opt-in — a subscription process that involves additional confirmation of the email address. This way, you will also protect yourself from addresses errors, spam traps, bots, and sneaky competitors.
Kirill Kolpakovich
Kirill Kolpakovich

Head of Antispam · Selzy

Double opt-in is great. Don’t be afraid that you’ll get fewer subscriptions. It doesn’t matter. What matters is that you’ll get more sales because, with double opt-in, you’ll be sending to those who really want to hear from you.

Personalize your emails

People who don’t do (email) marketing for a living often see any irrelevant emails as spam even if they had given their permission to receive them before. Instead of deleting, they would mark some emails as spam just so they don’t get them anymore. Easy for them but very undesirable for an email marketer.

So the best way to get into people’s inboxes is to make them feel special. For bigger impact, Create messages that take into account the personal data of the recipients, their preferences, interests, places of residence, and other factors.


Peloton has something for YOU. Source: Really Good Emails

It’s especially important for overheated and somewhat shady topics like cryptocurrency, for example, where email services get suspicious even if your emails, authentication, and reputation are in top condition. Bitcoin is legal but so many marketers abuse this topic that Gmail may block your campaign about crypto just in case.

The way out is to personalize your message and make them feel different from the rest and abstain from templates and cliches.

Add compelling texts to emails

Don’t see your campaigns as just another minor marketing technique you’re forced to use to make your subscribers buy something (albeit it is your aim). Make your newsletter shine on its own. Use copy that is engaging, interesting, and in line with a brand.

  • Create subject lines that match the content.
  • Check your spelling — spammers are known for their illiteracy.
  • Add Alt and Title tags to images to describe visual elements to users who can’t see them.
  • Prepare browser versions of emails for subscribers whose messages are displayed incorrectly.
  • Be extra careful with dubious topics like casinos, drugs, alcohol, bets.
  • Send something more than ads. Email marketing is a long-term relationship that’s about respecting users. If you’re useful, you’ll be able to sell and get recommended.

Tattly does a great job creating a potentially shareable email that features a sale and also an interesting-looking article. Source: Really Good Emails

Send regularly and consistently

Too many emails from one sender are one of the most popular reasons for people not reading them at best and marking them as spam at worst.

There’s really no one-size-fits-all approach here. Depending on your industry and goals, both daily (or even several times a day) and monthly frequency are good. In search of the right cadence, perform usual tests and try following the best practices. According to research, the majority of marketers send emails 2-4 times per month which makes once a week a good starting point:

marketers send emails

Image credit: Omnisend

It’s also best to pick a day and stick to a schedule. Subscribers (and email services) love it when you’re regular. In case there’s been a break or you are about to work with an old base, always send a message to re-introduce yourself first.

Segment big audiences into smaller groups

If you have a large email list, it means that your audience is likely to be more diverse and it’s hard to satisfy them all with one message. More people will neglect your emails, email service will start to mark your next messages as spam leading to poor deliverability.

The solution is to use segmentation to create subsets of your mailing list with common interests. Imagine you have an online store that sells wallpapers. Time goes by, the business is booming, you find yourself selling home furniture and mattresses also. If you continue sending offers about wallpapers to your entire list you’ll drive away customers interested in mattresses.

Segment the list according to subscribers’ preferences and interests, their gender, geography, age, family status and send different messages to each group. BTW, we have a guide on email marketing for small businesses, full of actionable advice.

Run email deliverability tests

Before sending. Create mailboxes in popular mail services and check how each of them reacts to your emails — whether they get to the inbox or not.

There is email deliverability software where you can view spam statistics before sending. For example, Litmus and Email on Acid have such tools.

After sending. Use the capabilities of email marketing analytics that find out what messages your audience finds more engaging.

Important things to avoid

And here’s a shortlist of no-nos that negatively affect your deliverability rate:

  • Don’t use link shorteners. Spam filters are suspicious of shortened links because they make you look like you’re trying to conceal the user destination. The same goes for regular redirects.
  • Don’t use spam lingo. Don’t draw attention to a topic with Caps Lock or exclamation marks.
  • Don’t create emails out of a single image. Practice tells that if an email contains less than 500 characters, it is likely to end up in spam. So pay attention to your image/text ratio.
  • Don’t buy lists. Here’s a fresh idea — to get fewer spam reports, don’t be a spammer. If you’re having trouble with building a list, get our epic foolproof guide on email list building.
  • Don’t add user-generated content in your emails without checking it first. You might be tempted to add some user reviews automatically but it’s dangerous to lose control over the content. Moderate every little bit of your emails.
  • Don’t use a personal address like [email protected] for mailings. Register a corporate one. A free domain says that a sender does not have a website. And if there’s no website, then there’s no company either. Then where did they get the email base?

What deliverability services ESPs have

Companies and marketers make their lives easier by using the services of email marketing platforms like Selzy that take over the majority of technical nuances so they don’t have to.

Here’s how we care about email deliverability:

  • We check the reputation of our IP addresses and technical domains.
  • We follow email authentication standards: DKIM, DMARC, SPF.
  • We track the reaction of users. If we see that some emails are blocked, we suspend a campaign.
  • We add unsubscribe links to all emails.
  • We do not send emails to recipients who marked previous emails as spam or unsubscribed.

Clients with the Standard and Premium pricing plans have the Recommendations feature where we automatically check each of their newsletters and suggest how to fix common mistakes.

Time to work on your deliverability

What to keep in mind:

  • There are 2 rates: email delivery and email deliverability. The former shows how many emails you were able to send successfully, and the latter is about how many emails got into inboxes.
  • Email deliverability is a very complex metric: it’s different with every email service so you won’t have a specific figure. What you can control is the number of emails that bounce and the number of spam complaints.
  • The major factors that affect email deliverability are the quality of your list and email content, authentification, reputation, patterns and anomalies.
  • If you feel that your deliverability is not OK, clean up your list, segment it, reduce the mailing frequency, check your authentication, and follow other tips from this article.

Good luck with your deliverability!

27 September, 2021
Article by
Kate Shokurova
Out and about, exploring the world and its marvels. A writer and editor with 10+ years of experience, I also dabbled in all kinds of marketing and am happy to use this experience to make quality content, useful for the readers and effective for brands. I feel really passionate about helping people understand about marketing and design through easily digestible materials. Outside of working hours, I enjoy hiking, dancing, watching movies and reading books.
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