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 all things email deliverability. Learn how to avoid that scary spam folder and deliver your messages directly into the inbox of your subscribers.

But first, let’s set the groundwork by defining the terminology we’ll be using so we are all on the same page.

Essential email definitions to add to your lexicon

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 gets 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 send to the junk folder.


Short for Internet Service Provider. A company that provides access to the Internet from a computer (AT&T, Comcast, Verizon, etc.).


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

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. 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 name.


Spamtraps are email addresses used by ESPs, ISPs, spam filter, blacklist providers, etc. 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). Spamtrap owners scatter these addresses over the Internet to see what sketchy collectors fall into their "trap" and use or sell these addresses. When a newsletter hits these inboxes, it means the email address wasn't collected legitimately and the list the sender's using might have been bought.

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 inspect 4 things.

Inspection #1: Email authentication

You can write “Amazon Support” as the From: name, but if your sender email address is “[email protected],” it’s pretty clear you’re not exactly who you say you are.

However, when you change the sender email to “[email protected],” it gets a lot harder for the recipient to reveal their true colors.

This is why email providers use email authentication protocols to catch fake news. 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 domain.

Inspection #2: Email reputation

As a sender, 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.

Signs of a healthy email list are:

  • Happy readers
  • Little to no spam complaints
  • A low bounce rate
  • No spamtraps on your list
  • No blacklist mentions
  • Regular, consistent distribution 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 engage with your emails. Good engagement metrics means people enjoy the content you send out.

With spam complaints we mean, users didn’t hit the “Mark as spam” button. Avoid spam complaints by sending high-value email content, using DOI to collect subscribers and not (correction: never) using purchased lists.

Spamtraps are bad news. It shows you’re tied up in sketchy practices or don’t scrub your subscriber list properly. Both spamtraps 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 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 send emails on regular intervals.

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 emails.

Meaning, if you use an ESP (like MailerLite) to send out your email campaigns, you have nothing to worry about. Make sure to enter the DKIM and SPF records to your DNS zone. You can obtain these records in your ESP dashboard. Adding them to your DNS zone can be done by you, or you can ask your ESP or web hosting service for assistance

The only thing to note 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 reputation (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. These IPs are perfect for senders who email corporate domains that are required to whitelist your IP address before sending them emails regularly.

Inspection #4: Email content

Your email content also affects your email reputation. Luckily, the rules for creating good email campaigns are fairly straight-forward.

  • Serve content that is valuable for your readers (think: does this really serve my audience?).

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

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

  • Use a business email ([email protected]) and not a personal email address (such as Gmail) 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, meaning subscribers should be able to get in touch with you.

  • Add an unsubscribe link in each email footer, so subscribers can easily opt-out. An unsubscribe is a 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 sketchy links using link shorteners).

  • Avoid spam filters by avoiding ‘spammy’ terms (more on this underneath).

Best practices: 3 things to improve the deliverability of emails

Avoid spam filters

Spam filters look at a variety of things. it’s important to:

  • Not use devious links (nor hide them with link shorteners).
  • Avoid ‘salesy’ words (check this list of spam-triggered words).
  • Not go overboard with exclamation points or ALL CAPS.
  • Highlight words in red. Other colors are fine, but spammers made the color ‘red’ a red flag.
  • Not have one big image as the email content. Add ALT text and short descriptions to images.
Separate the inactive from active subscribers

Want to increase your engagement metrics? Segment subscribers based on activity and create targeted campaigns to offer more valuable content. Active subscribers might be happy as is. Inactive subscribers can be encouraged to show interaction using a win-back campaign.

Use a sender address that is real and recognizable

Not just readers benefit from this, also spam filters use the sender address to check who you are. Use your real name or a consistent brand name in all your emails. Let people reply to an existing email address from a verified domain, such as [email protected] Business emails tend to have better deliverability.

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 away from blacklists and spam filters.

Cleaning up your list regularly with an email verification tool will maximize your email deliverability. 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?