Cold email outreach Guide

The guide to email deliverability

Published , Updated 9 mn
Profile picture for Axel Lavergne

Axel Lavergne

Co founder and chief editor

Axel is one of Salesdorado's co-founders. He's also the founder of, a review management tool for B2B SaaS companies

Email deliverability refers to the ability of emails sent to reach their recipients’ inboxes without a hitch. According to the definition of the ISPs (Internet Service Providers, which refers more broadly to email address providers such as Gmail, Hotmail, Orange, etc.), deliverability only measures the percentage of emails sent that have reached their recipients, without differentiating between messages arriving as spam and those arriving inbox.

In this guide, we will use a different definition of email deliverability: the percentage of emails sent that reach the recipient’s main inbox, not counting those that arrive as spam. After all, isn’t that what good marketers are most interested in, how many prospects see their emails go through their inbox?

From the moment it is sent to the moment it is received, the journey of an email is comparable to an obstacle course. But what are the different factors influencing the difficulty of this event?

How does email deliverability work?

It is important at this stage to understand the stages that an email goes through when it is sent.


  • When the sending server sends an email, it goes through the server’s anti-spam system, which checks that the message does not come from a blacklisted address or that previous mailings have been successful.
  • Once the email arrives at the destination server, the server may issue a NPAI (No Longer At Home Address – also known as a “bounce”) message to indicate that the address does not exist, and therefore the email cannot be delivered.
  • If the e-mail has correctly passed these first stages, it is then transmitted by the server to the recipients. During this transmission, it passes through the client antispam which will analyse the content of the message (HTML code, text, images)
  • If it is not considered spam, and the recipient does not bounce (e.g. if the box is full), the mail will finally arrive in the recipient’s inbox.
  • In the event that a reader considers, after reading the e-mail, that it should have been classified as spam, he or she can carry out the spamming himself or herself. This action will then have a direct consequence on the blacklist of the ISP concerned.
  • In order to monitor and deal with the various complaints related to his mails, the sender can have access to the feedback loop of the different ISPs. This will allow the sender to analyse which type of readers are complaining about his emails, and thus remove them from his lists in anticipation of his next mailings.

So we’ve gone through the whole obstacle course that your emails have to jump through to reach their destination.
In the rest of this guide, we’ll look at the various aspects of deliverability, how ISPs distinguish between good and bad performers, and what all marketers can do to ensure their campaigns reach the recipients’ inboxes.

Do you have delivery problems?

If you are reading this guide, you probably have problems with the deliverability of your emails. So, before talking to you about all the best practices to follow, we are going to present you with the solutions that you can apply in the short and medium term to improve deliverability.

Short-term steps

Case 1: You are blacklisted by an ISP

If only some of your emails are not delivered, it is very likely that some ISPs will blacklist you.
This means that they will systematically block your domain or sending address, and your recipients will no longer receive your emails.

  • Check your email deliverability rate by ISP and compare it to your average deliverability rate to detect blacklisting.
  • If this is the case, clean up your email database ( DataValidation is recommended for this) and contact individual ISPs to resolve the situation.

Case 2: You are blocked by your router

If none of your emails have been delivered, it means that you have been blocked by your router due to a high bounce rate, for example.
If this is the case, you will also have to show your router a clean bill of health and provide guarantees that your deliverability will be improved so that it agrees to lift your block. Indeed, the router has no interest in tarnishing its reputation by letting many SPAM messages be sent through it.

  • Tighten your customer segmentation on people who have opened your emails in the last 30 days, study the open rate by ISP and remove from your list contacts who have not been opened for over 18 months.

Medium-term approaches

Analyse your indicators by ISP

A common misconception is that the email deliverability rate is the same as the ISP accepting your email.
This is not the case. It is quite possible to have a 90% acceptance rate but a 10% open rate, as all the rest of your mail will be SPAM.
You should therefore consider email deliverability as the fact that it reaches its recipient, and not as SPAM.

  • Consider looking at the open rate per ISP and compare it to the average open rate to detect possible delivery problems.

Work structurally and iteratively on segmentation

We don’t remind you often enough, but the segmentation of your mailing lists is an essential element if you want to solve deliverability problems in the long term.
It is important to adapt the frequency and content to each customer group and their needs.
You will then send fewer emails to those who cannot handle too much pressure, and they will not report you as SPAM.

  • Regularly test segmentation by playing on different attributes of your customer lists.
Looking for more and better leads? Try Apollo, the leading sales intelligence & engagement platform

Best practices in email deliverability

Do you want to go further than just solving deliverability problems? Let’s take a look at the best practices to ensure that your emails arrive safely.

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The technical settings required for good email deliverability

1. Choose between shared or dedicated IP address

Email services keep a close eye on the reputation of IP addresses. To optimise your email deliverability, it is essential to ensure that your address maintains a good reputation. In email marketing, two types of IP addresses can be used:

Shared IP address

An IP address used by several senders.

  • Advantage: More affordable price
  • Disadvantage: Your reputation depends on the practices of other senders
Dedicated IP address

An IP address used by a single sender.

  • Advantage: You are the sole master of your reputation
  • Disadvantage: Higher price with no guarantee of better performance than a reputable shared IP

It is therefore understandable that the choice between shared or dedicated IP addresses depends very much on their reputation. If you are on a shared IP address, changing to a more expensive dedicated IP address only makes sense if your current reputation is bad. To find out what your current reputation is and decide whether or not you need to change, we recommend this article on how to find out your sender reputation.

2. SPF, DKIM and DMARC protocols

To learn more about these topics and to be able to use these protocols, you can read this article on the benefits of SPF, DKIM and DMARC.

Deliverability is a marketing job

As you can see, the reputation of your IP has an important influence on your deliverability. But it also depends on the reputation of your domain and your senderscore. To group these three notions together, we talk about sender reputation.
This sender reputation is directly linked to the engagement of your readers with your messages. The open rate, click rate and response rate are all parameters that need to be improved in order to achieve your ultimate goal: generating engagement.

Do you need prospecting files?

More than 11 million French companies
Information updated daily
Data from official sources
Enriched information (phone, email…)

To learn more about the best marketing practices to take care of your deliverability, we recommend you read this article on 29 ways to avoid spam.

The best tools for email deliverability

To complete this guide to email deliverability and the four steps to solving problems, we have chosen a selection of tools to optimise your emails and your deliverability rate.

Monitor your email deliverability

Poor deliverability doesn’t have to be the case: there are tools to check your configuration and reputation before sending your campaigns.

Clean up your customer database

Another important parameter to take into account and often unknown to the general public is the existence of all the email addresses of the recipients of your emails.

Indeed, sending emails to non-existent recipients will often cost you money and lower your deliverability rate.

Worse, it can damage the reputation of your shipping domain name. It is therefore essential to test the existence of email addresses in your contact list.

Tools to optimise the content and code of your emails

While it may not be obvious at first, the HTML code behind each of your emails has a direct influence on your deliverability rate and is not always the same as that used for a web page.

La redondance ou l’utilisation de codes non supportés par certains clients emails sont des écueils courants à éviter à tout prix.


Looking for more and better leads? Try Apollo, the leading sales intelligence & engagement platform

About the author

Profile picture for Axel Lavergne

Axel is one of Salesdorado's co-founders. He's also the founder of, a review management tool for B2B SaaS companies