The complete guide to email deliverability

Email marketing is frequently touted as one of the most rewarding marketing efforts in terms of ROI, but it’s far from easy. You can put in a lot of hard work to create and send offers, but if your emails don’t get through because of deliverability issues like being marked as spam, you have a critical revenue problem on your hands. People need to read and engage with your emails so your company doesn’t lose money and so your time isn’t wasted.

No other effort will help if your email doesn’t arrive when and where it should. As such, email deliverability is the most important factor to consider when looking to improve your email marketing strategy.

For example, if you’re seeing low open rates and bounces, these are signs your email deliverability isn’t where it should be and that it’s time to adjust. And if your emails are constantly being reported as spam, you need to take a good, hard look at why that’s happening.

There are no shortcuts — getting great deliverability takes time and effort. But in the end, it’s all worth it. Deliverability is where everything starts. As such, we’ve put together this white paper to help you improve deliverability to inboxes and apply best practices to all your email marketing efforts.

Let’s get started!



The vital importance of sender reputation

We can’t dive into a discussion about email deliverability without first talking about sender reputation, which is the most important factor used to determine email acceptance by internet services providers (ISPs) like Gmail, Yahoo!, or Outlook.

Also known as an “email sender score,” sender reputation is essentially a rating ISPs assign to any company or person that sends out email. A higher rating means you have a good reputation for reliability and following best practices, which means you’re more likely to see emails get delivered to your recipients’ inboxes.

On the other hand, if your organization has a lower sender reputation, ISPs are more likely to send your emails to spam or refuse to deliver them to inboxes in the first place.
For example, in 2016, Return Path discovered 21% of legitimate emails were sent to spam, with one of the primary factors being a negative sender reputation.

ISPs also use sender reputation data to determine what level of volume throttling (see section 2.4) to apply to your emails, or to work alongside other methods and processes such as spam filtering, authentication, etc.

A sender’s reputat ion is linked either to the domain or the IP address from which the emails are sent, or a combination of both. This is something akin to a credit score for email senders and is informed by a range of factors, which each ISP determines for itself (so you can have different sender reputations across different ISPs).
Some of the types of factors which affect your reputation include:

  • Volume of email that you broadcast
  • Number of bounce-backs you generate as a result of rejects and/or unknown users
  • Number of spam complaint notifications that you receive

Want to know more about reducing spam complaints? Read “how to easily avoid spam complaints.

Your sending domain

Let’s dive into some basics about sending email. For starters, in order to even send any email, you need a sending domain.

Domain Name Strategy

Your domain name is an important element for ensuring maximum deliverability.

By following these four rules when picking and setting up your domain, you’ll have a better chance of avoiding spam complaints from your recipients and being incorrectly filtered by ISPs:

  1. Use a domain name that links to your website. Example: YourAwesomeBrand. com should have @yourawesomebrand. com emails.
  2. Use the name of your brand as the sender of the email. Don’t use words like “admin,” “info,” or “contact.” Your recipients need to know where the message comes from. Also, never use a Example: Your emails should say “Your Awesome Brand” in the “from” section of recipients’ inboxes.
  3. Create different subdomains according to the type of emails you’re sending (commercial, transactional, newsletter, password reminders, etc.). Note that each one will inevitably end up having its own reputation score, which means that if you start having a problem with one, the others won’t be affected. Example: Have a newsletter.yourawesomebrand. com that you use to send only your newsletters from, and a promotions. for sales updates and events.
  4. Make sure your email client is properly configured with emails that start with postmaster@, abuse@, etc. This is a standard best practice across the industry so mail system dysfunctions or random emails sent to these addresses are delivered to the right person at your company to handle the queries. Example: Set up postmaster@ and route it to your web admin or main customer service representative’s email.



Once you’ve set up your domain name, it’s time to move on to the next step, which is authentication. You simply can’t have a domain without it.

Email authentication is a technological verification of the origin of an email message, and it’s one of the many ways the email industry is addressing the challenge of spam. Authenticating your emails is important to secure a positive reputation and earn an ISP’s trust in your brand, with more chances an ISP will actually deliver your email.

Without email authentication, you will never see great email delivery. Plus, it’s just good to protect yourself against
phishing attempts or spammers trying to spoof your emails.

The three most important email authentication protocols that you should have in place are:

  1. SPF – Sender Policy Framework
  2. DKIM – Domain Keys Identified Mail
  3. DMARC – Domain-based Message Authentication, Reporting, & Conformance.

Want to know more about email authentication and DMARC? Read “DMARC, what it is and why it matters.

The right subscriber permissions

Now that you have your sending domain in place, let’s talk about subscribers and the best way to obtain them.

These days, it’s unacceptable to email anyone without their clear permission. So, although the idea of buying an email list might be tempting to reach a bigger audience, it’s definitely a bad idea. Delivery-wise, you’re more likely to run into problems because of bounces, complaints, and spam-traps. It’s also flat-out illegal for you to email someone without their permission due to regulations like the CAN- SPAM act and GDPR.

This is why single opt-in versus double opt- in emails are so important.

Single vs. double opt-ins

A single opt-in is when subscribers sign up via a subscription form, and are immediately added to your email list. A double opt-in is just like a single opt-in, but it includes
a confirmation step where the contact receives an email and has to confirm their signup. Using a double opt-in signup process is the recommended way to acquire new subscribers for your newsletter or email marketing.

This is because double opt-ins provide confirmation that a recipient actually wants to get your emails. So when an email is sent to the subscriber after they’ve given you their email address, they can re-confirm they are in fact the owner of that email address and that they do want to receive your newsletter.

Transparency is key during the opt-in process. Let the subscriber know exactly what you’re going to send them, and how often. This will reduce the chances of you getting complaints, and it also eliminates the risk of getting bad, unengaged subscribers on your list (because a hard bounce or a spam bot will not confirm the double opt-in email).

Avoiding spam traps

It’s also important to use double opt-ins to gain confirmed subscribers if you want to avoid spam traps.

In essence, spam traps monitor, collect, and catch spammers. They’re fake email addresses that have been deliberately made available online, don’t belong to real users or administrators, and never actually send out communications.
These decoy addresses help ISPs track senders who bought and are using email lists full of people who haven’t actually given their permission to be sent emails. Many email lists that can be bought online today are purposefully set up as traps by anti-spam companies. Spam traps also help ISPs identify senders who have poor email list hygiene who haven’t recognized or paid attention to the fact that they’re sending emails to a fake email. In fact, ISPs are likely to send your emails to spam if your rate of unknown accounts/emails is 5% or higher.

Because of this, not only is it important for you to use the double opt-in method for obtaining subscribers, but you should also identify inactive or unresponsive users on a frequent basis.

For example, if an email address has been dormant for a long time, you should consider deleting it because it’s either a) an inactive user or b) a trap (most spam traps won’t show engagement like clicks or opens). If you routinely manage your inactive subscribers, you’ll likely get rid of your spam traps, too.

Running a campaign that asks existing subscribers to reconfirm their interest in your emails is another strategy to separate engaged subscribers from those who don’t confirm and might be spam traps.

Having a single spam trap in any of your email lists can destroy your email reputation and can even lead to complete blocks. So overall, this strategy shows you’re properly maintaining your email list’s hygiene and quality, as well as avoiding spam traps.

Want to know more about spam? Read “How to easiliy avoid spam traps.

Your subscriber’s expectations

Once your sending domain and opt-in process are set up, it’s time to move on to subscriber expectations around the campaigns you’ll be sending them.

Avoid complaints by meeting expectations

The most important factor for the success of your email campaigns is to maximize engagement with your customers. And one of the best ways to do this is to set clear expectations from the start.

When subscribers sign up through the double opt-in method, you have the chance to state the type and frequency of content you’ll be sending them. Basically, you tell them “what” they’re getting and “how often” they’re getting it.
This approach sets clear expectations for those who will receive your emails, which can increase the amount of engagement you see across campaigns.

Be relevant and valuable

You can increase engagement across your campaigns by sending out relevant, valuable content your subscribers are more than happy to open and read.

For example, when your customers sign up for your newsletter, they often share personal data and information about their preferences (demographics, location, main interests, etc.).
Don’t forget about this data! Use it to segment your list into appropriate groups and create relevant, compelling campaigns. By creating segments according to preferences, you can send targeted offers to each person and reduce the risk of your subscribers losing interest.

While it may seem harmless to send out an unrelated offer or marketing campaign, if you fail to meet the expectations your recipients have, you’re only going to shoot yourself in the foot and see a higher number of unsubscribes, and — even worse — spam complaints.

As an email marketer, you’re well aware of the dangers of spam complaints to your business, so do the right thing and keep your reputation and expectations intact. So when sending out an email, ask yourself the question, “Is this something that I would like to receive myself? Does it add value to my subscribers? Does it relate to their indicated preferences?”

Maintain proper frequency

Meeting the expectations of your subscribers also involves stating the frequency at which you plan to send emails.
Sending emails too often can be annoying for your subscribers and will result in your emails being ignored, even if the content is something they’d want to read. Although this won’t directly impact your email deliverability, it will affect your open rate and your ROI.

As well as being ignored, you also run the risk of unsubscribes and spam complaints. On the other hand, sending emails too infrequently disengages your subscribers and makes them forget about your brand or business.
Unfortunately, there is no magic rule when it comes to how often you should send emails, as this will entirely depend on your type of business, the email campaigns you’re running, and how engaged your subscribers are. On average, email marketers tend to send 2-3 emails per month.

Your most engaged recipients might appreciate a more frequent newsletter. On the other hand, you shouldn’t spam or nag the ones that are less engaged. Your best bet is to keep a close eye on your open and click-through rates, as well as the amount of unsubscribes you receive. Test different sending frequencies (within the expectations of your subscribers, of course), and see if there’s a sweet spot for your particular campaigns.

Your most engaged recipients might appreciate a more frequent newsletter. On the other hand, you shouldn’t spam or nag the ones that are less engaged.

Your best bet is to keep a close eye on your open and click-through rates, as well as the amount of unsubscribes you receive. Test different sending frequencies (within the expectations of your subscribers, of course), and see if there’s a sweet spot for your particular campaigns.

A closer look at your template

Before you push the send button, let’s take a closer look at your email template and what it should contain to help maximize your deliverability rates.

A clear sender

If subscribers don’t immediately recognize who an email is from, they’re more likely to hit the “spam” button. As such, make sure you use prominent, clear branding in the “from” address, the subject line, and the preview pane. The more prominent the sender’s brand is in these areas, the less chance there is that the subscriber will ignore your email.

Simple Opt-Outs

Simple opt-out options in your emails are incredibly important. By not only having this option in your footer, but also in your header, subscribers aren’t likely to miss it. Also, a one-click unsubscribe process is best to reduce further issues, instead of having recipients land on a form that asks them a reason for their unsubscribe.
Even if you don’t like the idea of losing subscribers, it’s always better to let them choose the one-click unsubscribe button over the spam complaint link.

Text-to-image ratio

While all spam filters operate differently, most email programs prevent images from loading automatically within your emails, which looks suspicious to subscribers (they won’t hesitate to delete or mark your content as spam). Additionally, spam filters will almost always block your content if it’s all images and no text. As such, you should aim for your emails to consist of 80% text and 20% images.

If most of your email content is included ina single graphic, add text to the footer area like your unsubscribe link, physical address, and more to help balance out the text-to- image ratio.

Spam trigger words

You should always be careful about the wording that you use in your email campaigns. In particular, you want to avoid as many spam words as possible, which is an ever-growing list of words or phrases that trigger the spam filters of most email providers. Spam filters are getting smarter by the day, and will easily kick your email to the spam folder if they pick up an overuse of these words in your content.

Blacklisted URLs

Blacklisted URLs are website URLs that search engines and related authorities like email providers block due to suspicious or malicious activity. As such, always make sure your message doesn’t contain any blacklisted links.

To prevent this, it’s best to avoid content or URLs provided by unverified third parties. You can test this by sending your email to a tool like mail-tester.

Want to know more about optimizing your template? Download our full guide to email deliverability in 2021.

Your IP strategy

We’ve covered quite a bit already, but there’s just a few more steps you need to take to ensure your email deliverability is at its peak performance. So for the next step of this process, start thinking about your IP strategy and its role in deliverability.

Sender IP addresses

IP stands for Internet Protocol, and your IP address is essentially a series of numbers and dots used to identify your activity connected to associated devices and/or domains. For example, your ISP provides you an IP address to your computer at home, and email service providers can assign you a different IP address when you start sending emails.

IP addresses are a way for ISPs to help determine the legitimacy of your email campaigns. They can get very complicated very fast, but for now, this is all you need to know about the relationship between email service providers and your IP address as an email sender.

Shared or dedicated IPs

Having a positive IP reputation is crucial for your campaign delivery. Just as ISPs pay attention to the domain you use to send emails, they also pay attention to the IP addresses you’re sending from.

As a smaller sender, you might have trouble building a solid IP reputation yourself because you need sufficient volume to get noticed by ISPs. So for senders who have smaller lists or send out fewer emails, shared IPs are the better option.
The risk of using a shared IP is that all your efforts to send good emails are meaningless if there are a couple of bad actors on the same IP. You must actively monitor shared IPs you send from to determine their deliverability performances.
Regardless, shared IPs are cheaper to maintain and many email providers canalso help you by keeping your content in the same sending group as brands with similar content (known as a “sending pool”).

For everyone that sends more than 2500 emails a day, a dedicated IP is preferred.
A dedicated IP means just that — an IP address for your exclusive use.
Dedicated IP addresses cost more than shared IPs, but you are the only person or organization whose reputation you have to worry about. All activity, good and bad, is solely related to how you use the IP address. For most larger businesses, a dedicated IP is the best option.

Want to know more shared or dedicated IPs? Read “Shared vs Dedicated IPs.

IP warm-up

An IP warm-up plan is critical to ensure ISPs will regard you as a legitimate email sender, since when they detect emails from a new IP, they often get suspicious.More often than not, a fast-paced and unplanned “big volume” approach leads to blocks and rate limitations, so your approach to the warm-up process plays a crucial role in how ISP monitoring systems label your IP address.

Opting for a conservative approach, with gradual builds in volume over time, will mean that rate limitations and blocks will only occur if the engagement is poor, the complaint rate is too high, there is bad content, or a bad quality email list is used.This means by sending emails to engaged recipients first, you’ll boost your reputation more safely and consistently due to the high email engagement.

When selecting your volume, make sure that it’s divided over multiple ISPs. Start with your most engaged subscribers, preferably those who opened or clicked in the last 30 days.For exact volume numbers, it’s recommended to follow this IP warm-up scheme.

Bounces, complaints and blacklists

Once you start sending emails, it’s important to keep an eye on how your campaigns perform in order to improve overall deliverability. As such, you need to watch out for two key indicators something may be wrong with your sending: bounces and complaints.

Bounces are any email that’s been rejected by your recipient’s mail provider and was sent back to you. Complaints are (inherently!) self-explanatory. Both can get you blacklisted by email service providers.

Want to read more about bounces, complaints and blacklists? Road “What is what: Bounces, complaints and blacklists“.

The role of engagement in success

Subscribers who open your emails and click through are the ones you absolutely need to keep track of during your email campaigns. They are of course responsible for your ROI, but also contribute to your sender reputation.

ISPs and engagement

Over the last few years, ISPs have relied more heavily on the engagement of email recipients as a key factor for whether or not to deliver emails to the inbox. Each provider determines what they consider “engagement,” but most include at least the open and click-through rates (CTR) of your campaigns.

If you can aim for a healthy open rate, you’re more likely to see your emails delivered. Good open rates differ by not just the type of email but also by the type of industry.

Hubspot, for example, found in a recent study that a good average open rate is 20.94%, with the electronics industry hitting around 19% and real estate averaging at 26%.

Likewise, click-through rates will vary by email type and industry. Hubspot discovered the average CTR across surveyed industries was 7.8%. Financial services saw the lowest CTR of 6.82%, while manufacturing hit an impressive 9.31%.

Inactive subscribers or non-responders

While you want to pay close attention to who’s opening your emails, you also want to take note of who’s not. That’s because inactive subscribers can be one of the biggest drawbacks to the success of your email deliverability rates.

Subscribers can become unresponsive for a number of reasons. More often than not, your email gets lost in their inboxes. Other times, they’re too busy to read your content, or their interests have changed entirely. At worst, they’re ignoring you because you did something to upend their expectations (e.g. you send more emails than you’d promised when they signed up).

Identify any inactive subscribers like these that you may have in your list, and choose one of two routes: reactivate or remove.

Some senders may want to choose the former tactic if they feel the subscriber actually does want to receive their content but were just too busy or missed the emails. If you take this route, consider lowering your email frequency to these subscribers in particular, or send them a message tied to your reactivation campaign asking them if they still want to get your emails.

If your reactivation campaign doesn’t get any positive feedback, your only choice is to stop sending emails to these addresses. Otherwise, you risk hurting your reputation by these addresses turning into spam traps.

You may feel frustrated removing subscribers from your list, but remember: it’s always better to put your overall reputation first and your total subscriber count second.

Evaluate and improve

Evaluating any negative issues that arise from your email campaigns is imperative to building a trusting relationship with both your existing and potential new subscribers.

There are multiple ways you can tell if something is not right: low open rates, too many bounces, lots of unsubscribes, spam complaints, getting blacklisted, etc.

Learning from these kinds of issues and dealing with them appropriately will help you avoid similar mistakes in the future, and therefore increase your open rates, ROI, and deliverability.