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Email deliverability guide 2024: Common issues and best practices

Reading Time: 10 minutes

Did your email engagement metrics drop significantly?

Emails bounce or end up in the spam folder?

It’s most likely that you’re having some issues with your email deliverability and email sender’s reputation. That’s quite a common challenge that marketers face when implementing their email marketing strategies. According to ReturnPath, 1 out of 5 emails never reaches the inbox—which can really impact your marketing performance.

When analyzing our clients’ campaign deliverability complaints, we see common mistakes that most clients make.

There are certain things that you should know when switching your email service provider or initiating a new email marketing strategy. So carry on reading to learn how you can fix your email deliverability and avoid this headache in the future.

What is email deliverability?

Email deliverability is the ability to deliver emails to your recipients’ inboxes.

Determining your email deliverability is quite complex. It depends on many elements, such as the service provider, sender’s domain, quality of email list, email frequency, IP reputation, and overall sender’s reputation profile.

It’s vital to mention that email deliverability isn’t the same as a delivery rate. Delivery rate indicates what percentage of your emails is received by your subscribers’ mailboxes in general, even if they land in the spam folder. Meanwhile, deliverability is the inbox placing indicator.

So, it’s possible that even if you have a sound delivery rate, you can still have deliverability issues.

What is a good email deliverability rate?

It’s difficult to define what a good email deliverability rate is. Return Path email deliverability statistics show that “just 79% of commercial emails land in the inbox.” The rest is “either sent to a spam folder or goes missing—most likely blocked by the mailbox provider.”

The goal of every marketer is to get an email delivered to 100% of subscribers. Unfortunately, very seldom do marketers achieve such a high rate.

You should pay attention to the following metrics when you track your overall email deliverability:

Partially, your email deliverability depends on the platform that you use for sending emails. All email service providers have different delivery rates. Most often, they fluctuate between 88-99%.

At Omnisend, we have a separate dedication for email deliverability and we pay a lot of attention to maintain this score as close to 100% as possible. Currently, our deliverability rate fluctuates between 98-99%.

If our clients follow the best practices and start sending email campaigns by warming up their senders’ reputation, they can get deliverability close to perfection.

Omnisend has also introduced our new Email Deliverability Reports, which show you ways that you can improve your deliverability for your contacts. This includes email list hygiene, using a custom sender domain, and changing your sender email address:

Omnisend users can now find all the information related to their deliverability in one report. This is particularly helpful since deliverability is complicated, and different customers have different needs and approaches.

The new Deliverabilty Report will show different colors, labels and information to give Omnisend customers personalized recommendations on how to improve their deliverability.

If you’re an Omnisend customer, you can get your Deliverability Report here. And if you’re not a customer yet, you should sign up now to see how we can improve your deliverability (plus get you more sales).

What are SPF and DKIM?

When talking about email deliverability, you’ll often hear the terms SPF and DKIM. Let’s look at each in turn and why they’re so important for making sure that your emails land in your recipients’ inboxes. 


SPF stands for the Sender Policy Framework, and it’s an email authentication protocol that allows the domain owner (usually the store owner) to specify which mail servers they’re using to send emails. Essentially, the SPF states that any emails coming from this domain will be using these mail servers. The SPF record lists which IP addresses are authorized to send an email on behalf of the specified domain.

When sending an email, email providers will do an SPF check where they verify the SPF record. In the SPF check, they look to see if the IP address used to send the email is listed in the SPF record. If it is, then all’s fine—but if it isn’t, then the messages will fail SPF authentication and the email will be blocked. 

image explaining how SPF works

SPF records are very important to block spammers and phishers (the bad guys) from emailing your recipients and pretending to be you. These forged emails will more likely be blocked from reaching your subscribers’ inboxes, ending up in the spam folder instead.  

In terms of email deliverability, an SPF-protected domain is less likely to be forged, and therefore less likely to be blacklisted by spam filters. That means that domains with an SPF record will be more likely to reach recipient’s inboxes.


DKIM, or DomainKeys Identified Mail, is a protocol that allows a company to take responsibility for sending a message, which can be verified by email providers. This is a bit more complicated than SPF above, since DKIM involves cryptographic authentication. 

But essentially, DKIM lets the company take responsibility for a message while it is in transit, making the message easier to trust (if it’s a normal company with a normal domain). If the company or its domain has a poor sender reputation, and therefore more likely to be blacklisted, DKIM won’t help much. 

explanation of how DKIM works

The advantage for you, the company, is that your recipients can verify through their email providers the legitimacy of the emails, allowing domain-based blacklists and whitelists to be more effective. 

Again, much like with SPF records, using DKIM means spammers/phishers are less likely to forge mail from your company. This would mean a lower chance of the domain being blacklisted, and a higher chance of the emails ending up in your recipients’ primary inboxes.

You can read more about SPF and DKIM records here.

What is IP warming?

IP warming is a process when a sender gradually increases the volume of messages sent with one IP address. It’s necessary for establishing a reputation with internet service providers.

If your sender’s reputation depends only on you, IP warming usually depends on your email service provider. Email marketing platforms cover the IP warming process because they have a lot of shared IPs for their clients and take care of them all.

Only companies with a huge sending volume that reaches 1.5 M emails per month start using their own dedicated IPs and start warming them by themselves. Read more about shared and dedicated IPs here.

Building your sender’s reputation

A sender’s reputation profile plays the most significant part in the email deliverability. So let’s dig deeper and figure out what it is and under what circumstances should you implement reputation building processes into your strategy.

What is a sender’s reputation warmup?

Reputation warmup is a process of improving your “reputation profile” so that you avoid the SPAM folder. You do this by gradually increasing the number of emails you send out based on a specific schedule.

Reputation warmup is highly recommended if your subscriber email list is higher than 50,000 contacts.

This procedure is typically done when:

  • you’ve just moved from one email marketing service to another one, thereby gaining a new dedicated IP address
  • you’ve just started with email marketing

It’s also vital that the subscribers in your first few rounds are pretty active.

This means that they’ll be more likely to open your emails and click them, which sends a good signal to Gmail, Outlook, Yahoo and other providers that your content is quality and your IP address can be trusted.

How should you get started with reputation warmup?

Gradually increasing your email volume helps you build a good and strong email sender’s reputation.

Warm up sending volumes and segmentation recommendations:

Campaign 15,000Placed order once in the last 7 days
Campaign 27,000Placed order once in the last 14 days
Campaign 310,000Placed order once in the last 21 days
Campaign 413,000Placed order once in the last 30 days
Campaign 516,000Placed order once in the last 45 days

It’s also a good practice to segment out those contacts that haven’t opened a campaign in the last 12 months. Learn more about that here. And don’t even import them to the new email marketing platform, at all. They will damage your sender’s reputation on the new platform.

Here’s a sample sender’s reputation warming schedule for a client if he/she has 50,000 recipients in total:

Email IP warming

Email deliverability issues

What are the factors that negatively affect email deliverability?

#1 A high complaint rate

If the email is unwanted, people will mark it as spam. This is one of the primary factors which lower the sender’s reputation. As a result, all your emails might start landing in the SPAM folder. Therefore, try to avoid spam complaints as much as possible.

#2 A high bounce rate

This usually means that the list is outdated, low quality, or contains email addresses that were purchased. Inbox providers treat such senders poorly and affect their reputation.

#3 Low engagement

If a subscriber received 50 emails but did not open any, this is just another signal to the inbox provider that the sender is not following best practices.

Therefore, more and more of his/her emails will be placed into the spam folder. Again, check for how the email addresses were collected.

Saying “goodbye” to inactive contacts is always a good thing, rather than waiting for them to unsubscribe. There are some good practices on how to do it in a smart way. Learn more about that here.

email sunsetting frequency

We’ve seen multiple times when a smaller active email list of 10,000 contacts drives much more sales than 50,000 (because 40,000 contacts were inactive and those bad contacts were damaging the sender’s reputation). Plus, sending emails to inactive contacts isn’t cost-effective.

#4 Too frequent campaigns

Even high-quality subscribers might be overwhelmed by receiving too many campaigns a day and will mark your emails as spam. Some will even unsubscribe from your emails.

The ideal frequency is 2-3 times/week. For daily senders: no more than once a day (with rare exceptions when there is a super rare once-in-a-quarter sale, etc.).

#5 A sudden increase in the number of emails sent

If a sender is usually sending to 50,000 subscribers and then starts sending to 150,000, this spike will cause more emails to be sent to the spam folder (because inbox providers consider spikes as an unexpected behavior and spam attack).

If you want to increase your mailing list size, do that gradually.

#6 Constantly switching between different email service providers

This hurts your sender reputation because the inbox provider might start seeing the sender as a spammer who’s trying to hide his/her trail.

Improve email deliverability: Best practices

By improving your reputation profile, you will increase the success score. These are email deliverability best practices to achieve that.

#1 Send emails to a highly engaged email list, with a high click rate

The threshold here for “high click rate” will depend on the industry you’re in. That’s why subscriber segmentation will be your best friend.

For ecommerce that sells apparel, small electronic devices, books or household pieces, the average click rate is 5-6%.

#2 Make sure the email is wanted

This means that the subscriber explicitly agreed to receive an email. That’s why lists must be opt-in and preferably GDPR-compliant.

If you notice a high unsubscribe rate, you might want to check how the email was captured in the first place.

#3 Gradually increase sending volume

As already discussed, if you have 500,000 emails in a list, starting your email marketing by sending campaigns to all of them immediately is a really bad idea.

If you start sending large batches on day one, inbox providers might see this as a threat and a spam attack. Therefore, your email will automatically be marked as spam.

#4 Keep your contact list clean

Statistically, 30% of subscribers change email addresses once per year. So you should clean and take care of your email list periodically.

If someone hasn’t interacted (clicked on your emails) in the last 12 months, that contact should be treated as inactive.

Such emails might later become spam traps. If a trap receives emails, this tells inbox providers that the sender isn’t following email marketing best practices.

As a result, your reputation suffers.

Pro tip: when you migrate from one email marketing platform to another, at first migrate your best contacts who are constantly opening and clicking your emails and start sending to them only.

That way you’ll gradually transfer your “reputation” from one email marketing platform to another.

After a while, you can migrate the rest of the mailing list.

Once again, migrate gradually. Start with a small list, then grow the number of contacts.

How to improve your email deliverability: a step-by-step guide

Essentially, there are a few things you can do today to make sure your deliverability and overall email delivery rate comes in at a good level. 

Step 1

Firstly, you should be using SPF and DKIM to ensure that mail providers can verify in one way or another that the messages are coming from you. That should help keep your email deliverability at a good minimum base level.

If you’re sending emails from your WordPress website, you can easily make sure SPF, DKIM, and DMARC are correctly configured on your domain with a plugin like WP Mail SMTP. If any of your DNS records are missing or broken, WP Mail SMTP will alert you right away so that you can fix the issue.

Step 2

After that, you need to make sure you’re sending emails only to those contacts who want to hear from you. That means that proper list management is key: clean your lists on a regular schedule, every 6-12 months or so.

Step 3

Beyond that, you should make sure that the content of your emails match your recipient’s expectations. This includes not just the content of the emails themselves, but also the content that will make them decide if they want to open the email or not: the subject line.

Subject lines are really important, since within 7-9 words you need to convince your recipient that they should open the email. But it goes even beyond that: some keywords in your subject line can land your emails in the spam folder, which will hurt your open rates, click rates, and campaign.

In total, good subject lines can equal good open rates, and that in turn will help improve your email delivery and campaign results overall. 

If you want to learn the best practices when it comes to crafting solid subject lines, head over here.

Key takeaways

Email deliverability is a metric worth keeping your eye on. You can’t build it in a day but you can ruin it within the moment you send the reckless email campaign.

And even if it happens, these are the essential things on how to grow and improve email deliverability rates:

  1. Try testing email deliverability using one of many email deliverability tools
  2. Implement a sender’s reputation warming
  3. Keep your list clean
  4. Segment your lists to get the best engagement rate possible
  5. Be patient.
Join a platform that actually cares about your deliverability. Sign up for Omnisend today.
Article by
Karolina Petraškienė

Karolina is a writer, content marketer, and email enthusiast at Omnisend. When she's not curating articles, you can find her in the woods challenging herself in hiking boots or off-roading her bike.