Entregabilidad de correo electronico

According to the Data & Marketing Association (DMA) it is estimated that the ROI of email marketing is 35€, meaning that for every 1€ invested 35€ is generated. This way, email marketing leads in the ranking of all digital channels.

Despite all of the technological advances, email is one of the most important channels, which is why staying up-to-date on the deliverability characteristics of email marketing is so important.

Below we have prepared the most complete guide to email marketing deliverability and in this way help you deliver your emails to the user´s inbox. We reveal all the essentials that you need to know in order to understand how does deliverability work.

How to improve email deliverability? 

If you are reading this article it is because your goal is to improve your ability to deliver a higher percentage of emails to users’ inboxes. At this point it will be important to keep in mind the role of ISPs and ask about their scope.

Do you know how many emails per day are sent around the world?  

About 260 billion. More than a half of those emails are commercial, the rest are from consumers. From the total number of emails about 100 billion emails land in Spam folder (as you can see we are talking about almost half of the total).

The ISPs (Internet Service Provider) are responsible for managing this avalanche of Spam. It’s objective is to make sure that Spam emails don’t reach even the unwanted folder and in this way guarantee a correct experience in the channel.

At this point, it is important to think like an ISP, this way we can ensure that emails reach users’s inbox. You have to bear in mind that ISPs have a history of user behavior with all emails (clicks, opens…) and inf no one interacts with your email it will definitely not be delivered.

In this best practice guide we are going to cover all the issues that affect deliverability.

What is the goal of email deliverability?

Let’s assume your emails have a delivery rate around 95%. At first glance you might think it’s a very good ratio, right?

We are leaving out an important point, which is that your goal is not only a high delivery rate, but also that your emails reach inbox, correct?

The main goal of email deliverability is to guarantee a good position of the emails in users’ inbox of the different domains.

We need to keep remember that an email that reached the Spam folder is also considered as delivered.

Understanding the journey an email makes

Imagine you have created an email for a specific campaign. Next, we will see all the steps of an email journey. First of all, it will be necessary to have a list of users whom we can communicate via email.Entregabilidad de correo electronico email marketing

1. Sending an email:

Envio de correo electronico

In principle, a large part of emails will be sent, though some of them may be supressed for various reasons (by the ESP, among others).

2. Delivering the sent email:

In general, out of the total emails sent, the mayority of them should be delivered, however, what happnes with hard bounces and soft bounces? 

Soft bounces

Hard bounces

 – Inbox is full    

–  Sudden increase in sending volume    

– Frequency too high for participation levels

– Email address does not exist or is not valid

What is a hard bounce?

Hard bounces occur when an ISP detects that the email address is invalid. If we look at it again from the point of view of an ISP, we can undesrtand that if there are many hard bounces the email list is not clean. A good practice is to regularly clean the email list.

What is a soft bounce?

Soft bounces occur when a valid email is not delivered temporarily for various reasons. Once the issue has been detected the recipiend will be able to receive emails again. What can often happen is that there is a sudden increase in sending volume.

3. Email has been delivered but it can reach inbox… or not. 

Entregabilidad de correo electronico

What is a Spamtrap?

Spamtraps are addresses that are monitored by email providers (for example Yahoo, Google, among others) in order to detect fraudulent mailing lists. In any case, it shouldn’t be on the mailing list.

4. Emails in the inbox can be opened or not.

Envio de correo electronico

When is an email considered open?

Through the tracking pixels we can detect when an email has been opened, this allows the service provider to know if a user has opened the message.

5. Finally, the recipient performs an action with the email.

 Finalmente, el destinatario realiza alguna acción con el correo electrónico.

Different actions and their meaning:

It was clicked. Your customer clicked on something in your email. This shows commitment and is probably what you expect them to do with your emails.      

No click. Does not affect the ISPs. Really low engagement is a sign that you need to work on your content. A good practice will be to increase personalization. 

Unsubscribe. The ISPs understand that people’s preferences change and that unsubscribing will not have a huge negative impact on their reputation.

Marked as spam. This is a very important factor for the ISPs. Your goal is to avoid many spam complaints. Customers can mark an email as spam if it is difficult to unsubscribe, so make it easy for customers to unsubscribe. You also want your consent page to be easy to navigate – if customers get confused or lost on your consent page, it is much more likely that they simply mark your email as spam and finish it. Respect your customers and make it easy for them to unsubscribe.


Email deliverability: Who’s involved?

There are three elements are needed to send an email to a customer’s inbox: senders (that is, the company that sends the email), gateways (the companies that allow you to send an email), and recipients (that is, the client).

Entregabilidad de correo electronico

Senders (company that sends emails)

We can generally divide email senders into three categories: legitimate email senders, email certification providers, and spam senders.

Legitimate email senders. These are companies that have a legitimate reason to send emails. These can be transactional emails, marketing emails, newsletters, etc.

Email certification providers. These are not exactly senders, but providers that can help get your email to your clients’ inbox. These companies often have good relationships with ISPs and can vouch for you as a sender, helping you bypass ISP filters. Their services typically require a monthly membership fee, plus you need to establish yourself as a trusted sender.

Spammers. People who send unsolicited messages, usually to a large number of people. They can be malicious (sending malware, phishing emails, other scams) or just plain annoying. They are the reason why ISPs have to be strict.

Gateways, companies that allow you to send an email

Gateways consist of ISPs and other companies that control whether your email is delivered. Usually there are two categories of ISPs: major Internet service providers and smaller providers (including small regional providers). Here we will also include anti-spam systems and blacklist organizations.

Major ISPs. From a deliverability point of view, you mostly have to worry about the major ISPs. If you can achieve deliverability with them, you should be fine with the lesser ISPs as well.

Minor ISPs. Smaller ISPs often use versions of the processes and algorithms that major ISPs use to monitor email delivery.

B2B anti-spam systems. Each company configures its anti-spam system differently, so it is very difficult to create guidelines on how to achieve deliverability with them. The good news is that business addresses are rarely used to sign up for e-commerce mailing lists, so these are not much of a concern.

Blacklist organizations. These companies provide reports about senders they believe are showing poor sending practices. All major ISPs use these reports, which means you don’t want to end up in one. If you do, you should make it your first priority to get off it.


Those are the people that you want to receive your emails. ISPs want to protect them from spammers, so you should follow best practices to get to the inbox. That means understanding the tools ISPs use to fight spammers.

How can ISPs affect email deliverability?

ISPs have several ways to control spammers. Since they have to manage a massive flood of emails, these tools can also negatively affect deliverability. Let’s see what those tools are and how you can manage each of them.

  1. Sending limits
  2. Blocks
  3. Email Bulking
  4. Blacklisting
Sending limits

ISPs set a sending limit for each sender. This is the amount of email they think is acceptable and normal for you to send in a given period of time.

Once you reach your sending limit, ISPs will gently bounce all emails you try to send until the limit is reset.

For some senders, this could be a weekly sending limit. For others, it could be a daily sending limit. This depends on the volume of email you send regularly. If you usually send emails once or twice a week, you will have a weekly sending limit.

It doesn’t matter how good is your reputation, if you suddenly increase your sending volume your emails will be gently bounced.

How do ISPs manage sending limits?

If you want to avoid your emails bouncing softly then you need to slowly increase your sending volume.

Let’s say you want to run a large Black Friday campaign, with a significant increase in sent emails. You should start slowly increasing your email volume at least 30 days in advance. Do this by gradually raising your sending volume so that you reach your target volume in time for  Black Friday campaign.


Blocked means you can’t send any emails. ISPs generally block senders after receiving too many spam complaints or if a sender rejects too many emails.

Blocking can last indefinitely, but they generally take from two days up to a week.

Email bulking

Bulking means ISPs are sending your email to spam or junk folder by default. Since most customers do not regularly check their junk folders, most of your emails will not be seen.

How to know if your emails will end up in the spam folder?

It is almost impossible to know if your emails are going to end in spam from most email platforms. However, several checkups can be made.


Blacklist of IP addresses – cannot send emails to ISPs that filter emails based on that blacklist. It is a stricter form of blocking and lasts until you appeal to the blacklisted organization and are removed from their list.

It’s much easier to avoid ending up on a blacklist than trying to get off it. If you are on a blacklist, it should be your number one priority to get off it. You will need to demonstrate better sending habits and an improved mailing list, which are good practices anyway.

Negative and positive attributes of ISPs?

For ISPs, when it comes to email deliverability, the world is basically black and white. You can minimize the bad and maximize the good, this will be good practice.

Negative attributes

Bounces. Both hard and soft bounces are signs of bad sending habits. Hard bounces mean your email list is not clean. Soft bounces are a sign of sending inconsistency.

Spam complaints. ISPs want to stop spammers, which this is very bad for them. ISPs have a very low tolerance for spam complaints. You should set a threshold for spam complaints of less than 0.1% and strictly adhere to it.  

Your emails are marked as read or deleted without being opened. ISPs can see when subscribers mark their messages as read or delete them without reading them. This tells the ISP that the content of your emails is potentially spam, making it a negative mark on your reputation. It is not as bad as being marked as spam, but it is not positive either.

Positive attributes

Add to contacts / address book. This is a really outstanding action. It shows that the recipient wants to receive your and is very good for your sender’s reputation. This usually has a low conversion rate (as low as 2%), but you can find ways to encourage it for a big boost to your reputation.

Add a line in the body of your email that says something like “Add us to your address book to keep up to date with our best deals!” This is especially effective when big sales are coming, like before Black Friday.

Healthy open and click rates. Good senders send emails that are opened and clicked. We will talk about this more.

Which deliverability factors can you control?

Some of the following factors have a big impact on deliverability, while others are not as important as you might think.

The quality of your contact list. This is always important, but if you are a new sender or your IP is new, this is all the ISP knows about you.

The frequency and relevance of your emails. If you’re sending emails every day, the ISPs will be more strict with you. You definitely need to segment your mailing list. Do you send the same message to everyone? Is the content personalized? This will have a huge impact on engagement and therefore deliverability.

The content and format of your messages. It matters, but not as much as you might think. Spam messages from a sender with a high reputation will have fewer delivery problems than valuable messages from a sender with a bad reputation. However, it is good to avoid using spam tactics.

Sender reputation. Extremely important, but you can’t control it as much as the other factors above. It deserves more attention.

What determines the sender reputation?

Before we start it is important to know that it’s normal to fluctuate between “average” and “good” reputation. If you have a big campaign coming up and you need to send a lot of emails to a segment that is not as engaged, this will reduce your reputation a bit.

Sender reputation is a combination of two factors: IP reputation and domain reputation. These are calculated separately, but both have a big impact on deliverability..

What is intellectual property reputation?

All emails are sent from a computer or server that has a unique identifying address (your IP address). It’s easy to link this IP address to specific senders, so an IP address gives ISPs an easy way to track senders..

IP reputation is based solely on the IP address the email originated from. It is not related to the brand sending the email.

The IP reputation is what gets you to the recipient server. As an email sender, you typically have a dedicated IP address or send from a shared IP pool.

What is domain reputation?

The reputation of the domain is what gets you in the inbox. Unlike IP reputation, domain reputation has to do with the brand that sends the email.

Domain reputation can follow your brand even if your IP address changes or your email service provider changes. This can be a good thing if you’ve spent a lot of time building a good reputation..

Part of your domain reputation is your industry vertical. As a general rule, ISPs are tighter on financial and banking companies and more lenient on retail and travel companies..

In general, the reputation of the domain has to do with the type of sender you are. Do you segment your lists? Are you sending emails to inactive accounts? Do less engaged audiences receive fewer emails? These are all factors that determine the reputation of your domain.

One of the best ways to manage your reputation is to segment your mailing lists.


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Segmenting in order to increase email deliverability

Another very good deliverability practice is segmenting the mailing list into smaller groups, called segments. When sending emails, instead of sending them to your entire mailing list, you send them to specific segments.

There are many ways to create these segmentations, but we will share a way to divide your audience that will help you achieve maximum deliverability and best inbox placement.

Email segmentation for deliverability

Use data from your email service provider or your own analysis to divide your audience into following groups.

Segment: Without consent

These are email addresses that you have that have not consented to receiving emails from you. Under no circumstances should you send emails to this segment.

Recommended email frequency: do not email this segmento

Segment: New (<30 days)

Those are the emails added to your list in the last 30 days. This segment can receive a good amount of emails because the users are usually active. It’s a good idea to setup an onboarding flow to welcome new clients to your brand.

Recommended email frequency: 1-3 emails per week

Segment: Passive (31-90 days old, no opens or clicks)

These emails are 1-3 months old and users never opened or clicked on any of them. Due to the fact that the contacts are relatively new it’s still possible that they might engage with your emails. Nevertheless, if you’re a frequent sender you may want to mark again your emails so you don’t alienate this group.

Passive accounts should make up less than 2% of your mailing list.

Recommended email frequency: variable, do not try more often than 1 a week 

Segment: Active (more than 1 month, open or click during 90 days)

These accounts have shown recent engagement with your emails and are eligible for a relatively high email frequency. A healthy email list should consist of at least 40% active accounts. You’re in good shape if 65% or more of your list is active.

Recommended email frequency: can receive the highest frequency of emails

Segment: Expiring (more than 1 month, last activity 91-180 days ago)

Expiring accounts haven’t interacted with your emails in the last three months, but have had some activity in the last six months. They are starting to disconnect from you, possibly because you are submitting too much repetitive content.

Try sending new content to this segment and concentrate on good personalization techniques to achieve more engagement. You should also move this segment to a reduced sending frequency, you probably won¡t win them back by sending even more emails. 

Recommended email frequency: 1-2 emails per week (for high prequency senders)

Segment: Expired (over 1 month ago, last activity over 180 days ago)

These accounts lost interest in your emails. ISPs can see how often recipients interact with your emails, and if they notice that someone hasn’t been engaging in the last 6 months they usually send your emails to junk folder.

Addresses in this segments can also be spamtraps, due to the fact that ISPs start claiming abandoned email adresses after 180 days. If you keep hitting spamtraps you’ll get very negative marks on your sender reputation.

These email addresses bring very little income to your business. You should consider completely removing them from your mailing list or create a reactivation campaign in order to try to engage them again.

Recommended email frequency: 0 emails per week

Segment: Inactive (over 90 days old, never opened or clicked on your email)

Inactive accounts don’t bring income to your business and it’s unlikely to change in the future. You definitely souldn’t send emails to this segment because that lowers all your email metrics. Eliminating this segment from your list will automatically increase open and click rates and help to avoid spamtraps. 

Recommended email frequency: 0 emails per week, eliminate this segment from your mailing list

This segmentation can be used by senders of all sizes and from different industries. It’s also a good way to measure the status of your email list.

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