Understanding email deliverability

Deliverability in email refers to both the server-to-server delivery experience and the ability or reliability of that email landing in a person’s inbox rather than their spam folder.

Email deliverability focuses have evolved over the years, starting with spam content words then moving to IP reputation, and now a primary focus on domain reputation and a scoring of other smaller metrics.

Along the way have been the addition of various methods of strengthening authentication around senders to help provide better, more accurate responses.

While email deliverability has evolved beyond earlier focuses, each provider (like Gmail) still utilizes various focuses together into a scoring scheme specific to that provider’s preferences.

Despite such unique settings, in general, the best practices are much the same across the board.

It is important to note that while you may think of email deliverability as a technical challenge to hurdle, in truth most of the principles around strong email deliverability involve practices that engage positively with the humans receiving and reading the emails.

Important considerations (from most to least)

This section outlines in order of importance the best practices to protect your ability to land your email messages in your audience’s inboxes.

Domain reputation and user engagement

Sender domain reputation is the concept where a mailbox provider scores your domain’s sending quality based on how their users respond to your emails.

NOTE: Outside of Google’s free Postmaster Tool, most providers do not advise of a sender’s domain reputation, as it is used proprietarily internally in most cases. You can also explore engagement metrics to understand your standing with providers.

This internal scoring is very heavily weighted towards the negative as a default so that anything that does not include an open is technically a negative mark for your reputation, though in degrees from not-great (unopened) to outright bad (marked as spam).

This means that it becomes important to maintain a healthy ratio of engaged versus unengaged subscribers in your audience.


Setting up authentication creates a positive signal towards an inbox placement and helps providers know that they are more than likely hearing from a real person (you, the sender).

A lack of authentication can sometimes be a reason, in questionable filtering situations, for providers to err on the side of caution instead of inboxing the message.

Learn more about setting up authentication for your domain in your Ortto account under Custom email domains.

Audience build and maintenance practices

All the systematic tips and tricks are essentially built around the simple human experience of, "Is this email expected and wanted?" Your email campaign should be positioned in every way to answer that question.

Obtaining subscribers via transparent, reliable, and permission-based practices is the start-all for strong deliverability (not to mention a requirement in our Ortto acceptable usage policy).

Furthermore, maintaining a healthily engaged audience primarily affects most inboxing decisions and is what most strongly contributes to your domain reputation with a provider.

When setting up means to obtain more subscribers, make sure:

  • The form is secured with reCAPTCHA.
  • You are upfront about the planned use of the submitted subscriber’s information.
  • You do not utilize catchall/gating methods of coercion. A subscriber that doesn’t want or expect your emails will hurt your reputation and the experience of the subscribers that do.

To maintain a healthy list of subscribers, make sure that:

  • Response data for email campaigns are being monitored closely and change your marketing approach as needed.
  • The list of subscribers is being re-evaluated every couple months based on engagement activity, making sure to re-engage and/or remove subscribers that have not engaged in while (permission-to-send expires at 12 months of engagement).
  • The ratio of engaged versus unengaged subscribers over the last 90 days is no worse than 70:30.
  • You allow contacts to easily unsubscribe should they no longer wish to hear from you and (optionally) include a subscription preference center link in every email so that contacts can update the content they receive and/or the regularity with which they receive it.

Remember, audience build and maintenance is at the heart of email deliverability.

First, completely avoid, where possible, the use of any type of file/document links or general link-shorteners. PDFs, Google Docs, bit.ly (though not their custom-domain link shorteners) and more have consistently been used by bad actors to hide malicious content. Because of this, an email can be unexpectedly filtered or even bounced due to the security settings concerning these.

Second, whenever possible, try to use your own domain to host linkable content. Every domain used in links has a reputation with various providers and that reputation can affect the deliverability of your email. By using your domain alone, you are retaining more control over an unexpected reputation problem occurring due to a third party domain.

Third, never type out a link in the text of your email content. Always try to hyperlink it behind a button, image, or normal text. Because of redirect links being added to your emails for tracking purposes, the link in the text will look different than the tracking link, which looks suspicious to providers and can cause an undesirable filtering experience.

Send consistency

Sending on a regular basis trains both the servers and the human recipient to know and expect you. It’s a great way to retain reputation and teach customers to know when to expect you so that they go and look for your email if a filtering experience should occur.

With that said, sending too frequently can cause subscriber burnout, also known as email fatigue. The easy way to avoid that is to send at a realistic frequency to subscribers (most people don’t need more than 2 marketing emails a week, outside of special use cases).

Responsiveness to engagement data

The engagement data in your Ortto account is the most organic and useful data to help guide you in understanding what your audience does and doesn’t like.

By being responsive to your audience’s needs and desires, you will create a more happy and engaged audience base, which will teach the systems of the mailbox providers that your content is liked and expected.

Evolving with email

Just because you delivered to the inbox yesterday, doesn’t mean you will today. As email evolves, it becomes a more and more responsive experience that changes both positively and negatively depending on how well your send practices are maintained. Consistently evolving and growing your email sending practices to honor the needs, limitations, and expectations of your subscriber base will only fuel a better email experience in the days to come.

Final notes

As you can see there are quite a few things that go towards your email deliverability experience on a daily basis.

While it can seem complicated, it is important to remember that the decisions being made are around making sure that what is being received is desired and expected. It can be helpful to put yourself in the shoes of your subscribers and ask yourself what your expectations would be, and how you as a sender can meet those expectations. Remember, your place in the inbox needs to be earned — there’s no way around it.

If you come across a practice decision that you are unsure about, ask yourself if it is something that would help maintain an experience that is desired and expected.