Email deliverability: What it is and how it works (+ best practices)

Email deliverability. It’s one of those terms you will undoubtedly come across when you dive into email marketing. But what is it? How does it work? And how do I improve it? We’re here to break it all down in plain, simple English.

In this article, we’ll talk about all things deliverability. Learn how to avoid that scary spam folder and deliver your messages directly into the inbox of your subscribers. Plus, we’ll share best practices to improve your deliverability.

What is email delivery vs. email deliverability?

So, what exactly are we talking about here? Email deliverability refers to your ability to reach the inbox of your recipients. It’s also known as the inbox placement rate, the percentage of emails that successfully land in the inbox.

One important thing to remember: don’t confuse email deliverability rate with your email delivery rate. They’re two entirely different things! The email delivery rate is simply the percentage of emails received by the servers of your subscribers’ email providers.

Thus, you may enjoy a high email delivery rate from having your emails accepted by your recipient’s email servers. But your emails may be landing in their spam or junk folders, affecting your email deliverability.

How does email deliverability work?

When your email starts its journey and arrives at the gates of email providers like Gmail, Outlook, or Yahoo, the virtual “bouncers” will shake down your email for the following four things.

email deliverability - how it works

Inspection #1: Email authentication

When sending your emails, how do people know that you are who you claim to be? In this age of phishing, spoofing and scamming, it’s sometimes difficult for a recipient to look beyond the “From:” name and the sender’s email address in a message.

This is why email providers use email authentication protocols to catch fake senders. These protocols include SPF, Sender ID, DKIM, and DMARC. These tools look beyond the surface and match IP addresses to verify if the sender’s email address relates to the actual sending domain.

Thankfully, you only have to authenticate your domain once with an email service provider (ESP) like MailerLite or MailerSend. This tells the servers of the world that the email address you’re using to send emails is really yours. Thus, your email is less likely to bounce or end up in the spam or junk folders.

Inspection #2: Email reputation

Behind the scenes, your sender reputation is assigned a score by Internet Service Providers (ISPs) based on various factors. These include the quality of your email campaigns, their frequency, number of subscribers, and subscriber interaction.

The higher the score, the better your email domain reputation. Conversely, a low or negative sender reputation means that your emails are likely to go straight to the spam or junk folders—or not get delivered at all.

As an email marketer, you want to befriend ISPs. It takes a long time to build a good email reputation, and it can be destroyed easily. Just like a real-life credit score. A good reputation means you’re sending emails to people that opted in and want to read your newsletters.

Inspection #3: Email infrastructure

We’re not trying to make you an IT whiz, so we will keep this part simple. The email infrastructure has to do with the hardware and software that’s used to deliver your emails. This is all managed in the background by the provider of email marketing services.

If you use an ESP like our partner, MailerLite, to send out your email campaigns then you have nothing to worry about. Just be sure to enter the DKIM and SPF records from your ESP to your DNS zone. This can be done at the hosting provider of your domain name.

Inspection #4: Email content

As gatekeepers, ISPs constantly monitor and filter questionable, spammy and phishing emails for their customers. This means your emails need to be designed and written with an emphasis on quality to get into their good books.

ISPs look out for things like leaving out an unsubscribe link in the email. This is generally a sure-fire way of identifying spam. After all, you’re legally obligated to allow recipients to unsubscribe or opt out from future mailings.

So you managed to pass all four tests and dodge the virtual bouncers. Congratulations, you’ve made it to your subscriber’s inbox! Next, let’s see how you can improve your chances of passing the gatekeepers and landing in the inbox with every campaign.

Best practices to improve your deliverability

If you’re finding deliverability to be a hit-and-miss affair, not to worry. The key point is to make sure that you are delivering useful and timely emails to subscribers that have opted-in to your list. Here are some things you can do to pre-empt email deliverability issues.

Gateway spam filters look at a variety of things in your email content to decide whether it’s a genuine email that the subscriber wants to receive—or something that’s a nuisance. Hence, it’s important to write and design your emails with the following in mind:

  • Don’t use devious links or hide them with link shorteners.
  • Avoid “salesy” CTAs like CLICK HERE and use of special characters.
CLICK HERE spam email example
  • Don’t go overboard with exclamation points or ALL CAPS.
CAPSLOCK spam email example
  • Don’t highlight words in red. Other colors are fine, but spammers somehow made the color ‘red’ a red flag.
weight loss email spam example with red font colour
  • Don’t have one big image as the email content. Add ALT text and short descriptions to images.
PayPal phishing spam email containing mostly images.

Want to increase your engagement metrics? Practice subscriber segmentation based on activity and create targeted, personalized campaigns to offer more valuable content. Active subscribers may be happy as they are, while inactive subscribers can be encouraged to interact using a win-back email campaign.

If people aren’t interacting with your emails, it’s probably best to reduce the number of emails sent to them—or remove them altogether from your email list. This list pruning should be done regularly as part of your email list cleaning and scrubbing routine—and it spells good news for your engagement rates!

This benefits both readers and spam filters who use the sender address to check who you are. Use your real name or a consistent brand name in all your marketing emails. Let people reply to an existing email address from a verified and authenticated domain, such as [email protected] Business emails tend to have better deliverability because of this.

As mentioned earlier, calculating your sender score can be more an art than science. There are many factors that ISPs look at to assess your email sending practices. One thing you can do is to protect your email domain reputation by practicing good email list hygiene.

Also, look closely at how you are collecting emails. You want people that have opted-in to your emails for the worthwhile content that you’re offering. Ideally, your list should have all of the following characteristics:

  • Happy readers
  • Little to no spam complaints
  • Low bounce rate
  • No spam traps in your list
  • No blacklist mentions
  • Regular, consistent sending of email campaigns

By happy readers we mean subscribers that signed up using double opt-in (to show they intentionally subscribed) and/or reCAPTCHA (to make sure they’re not bots). Happy readers also reward your emails with high open rates. Good engagement metrics mean people enjoy the content you send out.

Low spam complaint rates mean that readers didn’t hit the “Mark as spam” button. Keep avoiding spam complaints with these best practices:

  • Explaining what subscribers expect to receive before signing up
  • Sending high-value email content
  • Using double opt-in to collect subscribers
  • Being GDPR-compliant
  • Not (correction: never) using purchased lists

Spam traps are bad news. It shows you’re tied up in sketchy practices or didn’t scrub your subscriber list properly. Both spam traps and bounces can be filtered out by regularly cleaning up your list with a tool like MailerCheck.

Blacklists are your worst enemy. These lists contain domains, servers, and IP addresses of email senders that were caught sending spam. At your first foul, you can still get off the list pretty easily. The more it happens, the more you need to start preparing for a junk folder future. That is, if your email gets delivered at all!

Lastly, try to send your email campaigns consistently and evenly distributed. Of course, there will be times that your email volume will spike (due to holidays or sale seasons), but try to settle into an email cadence that’s ideal for you.

What you may not know is that ESPs use shared IP pools for all their users. This means that all senders with the same IP contribute to the email deliverability score. For most senders, this is beneficial, as they can profit from other people’s reputations (and need to worry less about consistent sending and regular list cleaning).

However, if you’re a high-volume sender and want to be in total control, it’s best to use a dedicated IP address. This means your IP reputation belongs to you and you alone. These IPs are perfect for senders who email corporate domains that are required to whitelist your IP before sending them emails regularly.


When you get your shiny new IP address, it can be tempting to start sending bulk emails straight away. Avoid this mistake! You first need to establish your reputation with major ISPs to prove that you are a responsible sender: warm up your IP address by gradually increasing the sending volume over several weeks.

Meet their needs with relevant content and you’re on the way to creating successful email marketing campaigns. Here are ways you can optimize your content for deliverability:

  • Serve content that is valuable for your readers. Think: does this really help my audience?

  • Be consistent in your design so that people can recognize your brand.

  • Make your emails readable on desktop, tablet, and mobile devices. Most ESPs automatically make your email template responsive.

  • Use a business email (like [email protected]) and not a personal email address (such as [email protected]) when sending emails through an ESP.

  • “Do-not-reply” email addresses are a thing of the past and negatively affect deliverability. Email marketing is about growing relationships and subscribers should be able to get in touch with you whenever they want.

  • Add an unsubscribe link in the email footer, so people can easily opt-out. Let’s face it: an unsubscribe is 100 times better than someone marking your email as spam.

  • Don’t trick people! Align the subject line with the email content and don’t hide dodgy links using link shorteners.

  • Avoid spam filters by not using spam-like terms. Otherwise, the email algorithms will be onto you before you can shout “deliverability”!

You probably have a good idea of what your email delivery rate is, but checking for email deliverability might seem a bit more technical. Fortunately, there are easy ways to test your ability to land in the inbox, including:

  1. Sending a tester email to yourself: This is a quick, free way to see how your new email campaign looks in the inbox. But be warned—this isn’t 100% reliable, because an email that lands in your inbox might also land in someone else’s spam folder.
  2. Using an email deliverability testing tool: There are lots of testing tools out there that will scan your emails for spammy content, HTML errors, and check for a return path for bounced messages. Some even test how your emails will perform with different mailbox providers!
  3. Checking the design and responsiveness: The way your subscribers interact with your email can also be an influencing factor. You can improve email deliverability by testing for things like mobile responsiveness, and how the email looks in dark mode.

It’s always better to be sure before you hit ‘Send’, so when in doubt, test, test and test some more! And use a deliverability tool for that extra validation.

Essential email definitions to add to your lexicon

To finish up, let’s review all the terminology we just used about email deliverability so we’re all on the same page, OK?

Email delivery rate

When you click send, your email travels to the gateway server of your subscriber’s Internet Service Provider (ISP). The email is then accepted or gets returned as a soft or hard bounce. The percentage of the emails that get accepted is the email delivery rate.

Email deliverability

Your email arrived at the gateway server, but where will it land? Best case scenario, it gets delivered to the inbox of the subscriber. But, your email can also be blocked by a spam filter or sent to the junk folder.

Email list hygiene

Clean your email list from hard bounces, unsubscribed and inactive subscribers regularly to protect your sender reputation and improve your email deliverability. Use an email verification tool to periodically remove invalid email addresses, role-based and disposable emails for a higher quality list.


The acronym for Email Service Provider. A platform to send messages in bulk, manage subscribers, and track email campaigns (just like MailerLite).


Short for Internet Service Provider. A company that provides access to the Internet from a computer (AT&T, Comcast, Verizon, etc.). In email marketing, ISP generally refers to the big webmail providers: Gmail, Outlook and Yahoo! Mail.

Soft bounce

A soft bounce is a temporary issue. The message gets delivered to the recipient’s mail server (since the address exists) but gets bounced back undelivered. The reasons for this can be a full inbox, the message being too large, or a temporary server timeout.

Hard bounce

A hard bounce is a permanent issue. The email message returns to the sender due to delivery issues. This mostly happens because the email address doesn't exist (typo or out of service) or because the email is blocked by the recipient's server.


DomainKeys Identified Mail is an email authentication protocol. It allows the sender to cryptographically sign an email, so that mailbox providers can identify the sender when the email arrives. They take this information from the email header. Because the implementation is a bit of a challenge, not every sender uses it. That's why DKIM does matter, but it's not universally seen as THE way to reliably identify the sender.


SPF stands for Sender Policy Framework. SPF records are stored in the Domain Name System (DNS)—a virtual phone book, if you will. In this phone book, it says who owns a domain and who is allowed to contact people using this domain. SPF alone is not spoof-proof, as many websites use shared hosting (and thus share domain IP addresses). It does influence your deliverability but it doesn't guarantee inbox victory on its own.


DMARC stands for Domain-based Message Authentication, Reporting & Conformance. It's a virtual gate that senders can pass when both the SPF and DKIM are valid. Because DMARC combines the two, it's the most reliable technology to separate the heroes from the villains (cybercriminals, phishers, spoofers, etc.).

Sender ID

Sender ID is an authentication protocol framework that's very similar to SPF. The difference? SPF checks the "envelope" addressing (the technical part you don't see) but it doesn't check the header items (the From: part you do see). Sender ID enhances SPF by checking header items too. It recognizes when a sender tries to fool the recipient by altering the sender's name.

Spam trap

Spam traps are email addresses used by ESPs, ISPs, spam filters and blacklist providers to catch bad senders. These addresses are newly created (Pristine) or reactivated using inactive existing ones (Recycled). A third type is email addresses with typos in them (Typos).

Spam trap owners scatter these addresses over the Internet to see which shifty collectors fall into their "trap" and then use or sell these addresses. When a newsletter hits these inboxes, it means the email address wasn't collected legitimately and that the list was probably bought.

Recap: Email deliverability isn’t hard when you put your subscribers first

Email deliverability is a complex topic, but when you keep a few things in mind you’ll enjoy healthy inbox delivery time and time again. Set up your email authentication protocols, create high-quality email content that subscribers love to engage with, and stay far away from blacklists and spam filters.

Cleaning up your list regularly with an email verification tool will maximize your email deliverability. And don’t forget to run your campaigns through a deliverability testing tool. Remember: a smaller list with quality email addresses is much better than a huge list with harmful email addresses (not just for deliverability, but also for conversions).

Technicalities aside, the main takeaway is that as long as you send meaningful email campaigns to subscribers that said “yes” to reading your content, email providers will happily deliver your messages to the subscriber’s inbox. Not that hard after all, right?

I'm Megan, Senior Content Writer. Like MailerCheck, I love to simplify where possible. From Marie Kondo-ing my wardrobe so everything fits in the suitcase I never unpack to building websites with no-code. How do you make life easier?