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Improve Email Deliverability: Common Issues And Best Practices

Learn best practices to improve email deliverability and address common issues.

Did your email engagement metrics drop significantly?

Emails bounce or end up at the SPAM folder?

It seems that you have issues with email deliverability and email sender’s reputation. That’s quite a common challenge that marketers address while implementing their email marketing strategies. According to ReturnPath data, 1 out of 5 emails never reaches the inbox. So this issue might become significant in the overall campaign performance.

When analyzing our clients’ campaign deliverability complaints, we see widespread pitfalls that most clients encounter. But the best practices come to light as well.

You should know certain things when switching your email service provider or initiating a new email marketing strategy. So continue reading and learn how to fix your email deliverability and avoid this headache in the future.

What Is Email Deliverability?

Email deliverability is the ability to deliver emails to recipients’ inboxes. This metric is complex. It depends on many elements, such as 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. A delivery rate indicates what percentage of your emails is received by subscribers’ mailboxes, even if they land in the spam folder. Meanwhile, deliverability is the inbox placing indicator. It shows whether your email gets into the primary inbox of a subscriber. So, even with a sound delivery rate, you can still have deliverability issues.

What Is A Good Email Deliverability Rate?

It isn’t easy to define what a reasonable email deliverability rate is. Return Path claims that “just 79% of commercial emails lands 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 marketer achieves such a high rate.

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

  • 95% and higher is considered to be a good delivery rate on behalf of an email service provider.
  • The bounce rate shouldn’t be higher than 3%.
  • In terms of the SPAM rate, you shouldn’t be ringing the alarm bells as long as it doesn’t exceed 0.08%.

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, it 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.

What is IP Warming?

IP warming is a process which 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 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 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 Volume/Campaign Recommendations
Campaign 1 5,000 Placed order once in the last 7 days
Campaign 2 7,000 Placed order once in the last 14 days
Campaign 3 10,000 Placed order once in the last 21 days
Campaign 4 13,000 Placed order once in the last 30 days
Campaign 5 16,000 Placed 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 IP warming schedule for a client if he/she has 50,000 recipients in total:

IP warming schedule for a business with 50,000 contacts in total

When Omnisend client Chellysun switched from Recart to Omnisend, they used the following IP warming schedule to help improve their deliverability and ensure they stay out of the spam box.
The number of emails sent by Chellysun over time using the IP warming technique

As you can see, they didn’t follow the recommended schedule perfectly, so the difference between the 9th campaign and the 10th campaign was more than 80,000 contacts.

Nonetheless, by the 10th campaign (after carefully segmenting subscribers for the first 9 campaigns), their reputation profile had already increased.

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, your reputation suffers. Consider using a bulk email verifier to regularly clean your contact list to avoid potential issues and maintain a healthy sender reputation.

#2 A high bounce rate

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

#3 Low engagement

If a subscriber receives 50 emails but does 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.

Saying “goodbye” to inactive contacts is always a good thing. There are some good practices on how to do it decently. Learn more about that here.


We’ve seen multiple times when a smaller active 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.

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 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.

#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 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.

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. Implement a sender’s reputation warming
  2. Keep your list clean
  3. Segment your lists to get the best engagement rate possible
  4. Be patient.

This article was originally published by our friends at Omnisend.

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