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What are the links between deliverability and email content?

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You have just received the campaign you ordered from your email design agencyand that's when the stress starts: will my new size have an impact on my email deliverability ? Will the newsletter's contents land it in the spam box? Simplistically and without nuance, I'd like to say no. It's not your designer, your copywriter or your HTML integrator who will single-handedly make your deliverability levels falter.

But as you can imagine, there's nuance involved! A lot of nuance. Initially, I wanted to write an article on the subject of template development alone. Obviously, one thing led to another, and I ended up with an article as long as my arm. An article dealing with the relationship between email content and its eventual filtering in spam. Because on on the subject of deliverability, there are still plenty of legends to debunk.

This article has received numerous reviews and contributions fromdeliverability experts.

Table of contents: content and deliverability

Filter the content of your newsletters? No, protect your mailbox!

If you're reading this, it's because you want to apply good deliverability practices, not cheat. But sometimes, even with the best of intentions, spam filters catch you in their net.

Rest assured, this isn't a vendetta (at least not if you're sincere when you say you want to respect good practice).

More than just filtering out unsolicited e-mail, spam filters and the "Abuse" teams of webmails and ISPs are primarily there to protect users messaging systems. If your emails go to spam... it's maybe you look too much like a pirate or to a phisher.

From a security point of view, content is necessarily an important parameter: viruses, fraudulent links, identity theft... Everything is worth analyzing when it comes to detecting attacks and flushing out cybercriminals.

But you're not cybercriminals (well, I hope not). So let's show some white paws, you should always do exactly the opposite of what spammers do (the real villains)! Playing the transparency and virtue card is clearly the right strategy.

The main purpose of spam filters is to protect messaging systems.
The main purpose of spam filters is to protect messaging systems.

Content, one of many indicators for determining the deliverability of your mailings

At the beginning of the great spam adventure, there was SpamAssassin (I'm simplifying)! Back in the day, around 2000, spam filters had little choice but to filter on the basis of email content.

But today, those days are gone. We're talking about machine learning, behavioral analysis, working with mountains of data, historization... and a key concept has emerged: reputation.

A single criterion can therefore "rarely" land your newsletter in the spam box. (unless it causes you to exceed a threshold). It's a whole set of signals that are mixed together to decide on reputation and therefore classification by anti-spam filters.

To spice things up (otherwise it's no fun), each mailbox, each webmail, each ISP will use its own recipe and mix different tools. There isn't just one anti-spam filter, but a succession of anti-spam tools. Also, an e-mail may follow a different filtering path depending on its categorization, sector of activity and reputation history.

What signals do spam filters use?

Nevertheless, on basic spam (not the dangerous stuff we saw above), filters will try to answer a not-so-simple question with the means at hand: Do recipients want to receive this email?

(And as an alternative question: Is the sender of this email respectable?)

So the content of the email, yes, a little, but many more relevant signals come into play:

And lots more besides. Don't hesitate to read our deliverability best practices guide.

Local ISPs and webmails

Reputation has become a central concept in spam filtering. But it requires a great deal of data. These are the biggest players in email messaging, who have the opportunity to implement the most up-to-date mechanisms. In addition to size, local legislation can also reduce the volume of usable data and therefore the sophistication of reputation systems.

It is therefore important to know your target market. In some countries, the big American webmails will account for more than 80% of emails sent. But in others, this will not be the case.

Take France, for example. Even though Gmail is often the first destination for emails, local ISPs, and Orange in particular, continue to account for a large proportion of the audience. They have to comply with French and European legislation, which is more restrictive than in the United States, but they also have to work with fewer financial resources. Email content will therefore be more important in this case.

The case of B2B deliverability

One last remark before we get to the heart of the matter: the case of B2B! If major email destinations in B2C use modern techniques as explained above, in B2B it's much more varied.

It goes without saying that the anti-spam techniques used by a multinational and a small business will not have the same level of maturity.. That's why you need to be even more careful. Content-based anti-spam techniques are still much more widely used in B2B than in B2C.

The text, can the way an email is written cause deliverability problems?

Then yes! If the way your email is written makes you want to click on "This is spam", you're clearly in trouble. Creating disappointment, lying, being unnecessarily insistent... will necessarily create dissatisfaction. And then we come back to the previous point, disengagement, spam complaints, ... a tumbling reputation.

Do spam words have an impact on deliverability?

No, use the words "free", "credit"... or even "viagra". will not necessarily penalize the delivery of your emails. Just as writing a subject in capital letters won't necessarily cause your deliverability rate to plummet. (even though I know that the Internet is full of simplistic articles that will tell you otherwise, copying and pasting the same lists of spamwords for years).

Just think, even adult content arrives in your inbox (not all of it, though).

So words don't matter?

If the lists of spamwords circulating on the Internet are of very little valueBut that doesn't mean that words don't matter in certain circumstances. To understand this, we need to go back to the point about security. Every day, millions of fraudulent e-mails are sent out, trying to pass themselves off as legitimate campaigns. Hackers exploit many of the same tricks as marketers: news, sales pitches, etc.

As we've seen, spam filters are there to protect recipients from attacks. As a result, if a large number of phishing attacks use the same keywords as you, your campaigns may be sent to spam mailboxes... as a preventive measure. Bad luck, but good to know. Also consider periodicity. Certain terms will be heavily used by mass campaigns at certain times of the year. For example: blackfriday, sales, christmas...

Need help?

Reading content isn't everything. The best way is to talk to us.


In the same vein, some anti-spam programs use rules to block campaigns that have generated a large number of complaints. In order to detect them again, pieces of sentences, groups of words or an object are used.

Finally, it is important to think about the lexical field used. If you're a sock salesman, there's no reason for you to talk about Viagra in your emails. If you really want to, because you have a quirky brand tone, then you'll have to do a few tests.

How do you find your way around deliverability and spamwords?
What to do with spam lists? Take them with a grain of salt!

The impact of links and domain name reputation on your deliverability

In an email, there are links. Because you want people to click on them. These links inevitably use a domain name. And the reputation of this domain name has a significant impact on the delivery of your email. By the way, domain names aren't just found in links, they're also found in shipping addresses, in List-Unsubscribe URLsto call up the images displayed in your e-mail. By the way, images aren't just used to display beautiful visuals to your recipients, they're also used to track the number of times your message is opened.

So links and domains are essential.

The importance of domain blocklists

A blocklist email or blacklist, is a database of IP addresses or domain names. These databases are used by spam filters to block certain campaigns.s based on the IPs and domains used.

There is a very large series dedicated to sending IPs, but also a few for domains.

The most widespread is certainly Spamhaus DBL. If one of your domains is listed here, you've screwed up big time. Good luck with that.

But there are others that can have an impactHere are the most important:

Don't forget that each e-mail service will use its own recipe for filtering spam. The use of Spamhaus is fairly universal. For the rest, it depends on many factors (B2B/B2C, country, etc.).

How to avoid being spammed by a domain or URL?

Here are a few recommendations to avoid deliverability problems linked to the use of :

  • Don't just think about your own domains Do you need to link to a partner's site? Integrating a new visitor tracking system? Implementing a new analytics solution? Are you hosting your images on your router's server? These are all cases that can be tricky and affect your deliverability. Run these domains through blacklist verification tools such as MultiRBL.
  • Avoid mass-market url shorteners : They're used by many people, and not always for benevolent activities. If you really need a url shortener, try to find one that allows you to customize the domain.
  • Make sure you have an effective subdomain policy In-house, too, your organization's various activities may have more or less virtuous uses for your domain names. So be sure to group your different message types into distinct sub-domains and keep the number of different domains to a minimum. Ideally, you should only have one main domain in your e-mails.
  • Avoid linking to links : Okay, this one needs a little more explanation. As we saw above, it's important to distinguish between spammers and hackers. Malicious personalities include phishers who try to pass themselves off as someone else. The classic case (which speaks to everyone) is an email that looks like it's sent by Paypal, but isn't sent by Paypal at all. Filters therefore have built-in protection mechanisms. One of them is that a link must be what it claims to be. This means putting a site address in an e-mail, but clicking on it redirects you to a tracking URL. This is problematic. Example: <a href="https://track.sbm90.com/qzecrsdmvksnd">www.badsender.com</a>
  • Avoid too many links You don't need to put links on every element of your message. This may unnecessarily weigh down your code, or even anger some zealous filters.
  • It seems that some TLDs are causing problems (Top Level Domains, often called "extension"): By the way, to help us, Spamhaus maintains a that may be of interest to you. So if you're using .live, .zip or .fyi, don't hesitate to ask yourself a few questions.
Don't display links in your e-mails if they are tracked on click.
Don't display URLs in your content if the link to them isn't from a tracking domain. It's too much like phishing!

Can images get your newsletters into spam boxes?

La point the most important thing for images and deliverability is their hosting and the domain name used. As explained in the previous point, you'll need to make sure you don't choose shared hosting, or else personalize the domain name.

On the question of text/image ratio in emailingI recommend this article, published some time ago and still relevant today.

We can also talk about the weight of images. Image weight has little impact on deliverability issues, except when reaching extremes. It's important to know that anti-spam filters will carry out more or less advanced analyses of the images in your newsletters. This may involve character recognition (OCR) to check whether text is present in the images, or the use of artificial intelligence, etc. If the image is too heavy, the analysis solution may decide not to analyze it for performance reasons, and at the same time decide to penalize your message.

Too much weight can also cause your e-mail to display too slowly. In this case, engagement will be affected (see next point). But since you're paying attention to theeco-design of your emailsIt's not going to happen, is it?

Engagement is also about content, and therefore influences your deliverability

Your reputation in deliverability is built and maintained by your ability to engage your audience. If you like your message to your audience, engagement will be good, your deliverability will itself be better.

You need to be able to adapt to the specific characteristics of your target audience. For example, if you're targeting the elderly, you'll need to work on theaccessibility of your mailings.

This is not the place to talk about improving engagement in your emailing strategy. The Badsender blog is packed with resources on the subject. So we're going to focus on the main mistakes to avoid that could be part of a checklist for validating your email campaigns :

  • Sending the wrong message An email that's not finished, not proofread, not validated... is bound to be bad for your image and a waste of time for your readers.
  • Targeting errors We've all made them in our careers. Sending a newsletter to the wrong list, sending an email to the entire database when it was intended for a very specific segment. Again, bad!
  • Tone changes If you've been offering a homogeneous experience to your recipients for many months, suddenly changing it can have a double kiss-cool effect! It can be very positive, out of the ordinary, appealing and therefore generate good performance. On the other hand, it can be disappointing, disturbing, etc. There's only one solution: test it!

Can an email's html code affect deliverability?

It's a classic question, and the one that prompted this article. The way an email's html code is written doesn't have a direct influence on the way it's displayed. on its categorization as spam. But as always with deliverability, there are a few nuances to consider.

To repeat the same elements of good practice over and over again, the content of your e-mails should not resemble that of a spammer. Some anti-spam filters will therefore compare parts of your emails with those of other campaigns.

These email parts can therefore also include HTML code. This is what some people call fingerprinting.

It is for this reason that it is not not recommended to recycle email templates for acquisition or affiliation campaigns for loyalty campaigns. Acquisition and affiliation are generally very risky (very low engagement) and could have a negative deliverability impact on loyalty campaigns.

A few additional tips to avoid looking like a spammer:

  • Avoid hidden text White text on a white background, low contrast, hidden text in css... these practices should be banned in html email integration. The only acceptable case is hidden pre-header texts.
  • The weight There is no official limit to the weight of an email's html code. The main limit found in the literature is Gmail's 102kb limit, which is not strictly related to deliverability (the email is truncated), but which can have an impact, for example, if your unsubscribe link becomes invisible. As with the weight of images, the only limit will be that of the digestion capacity of anti-spam filters. Stay moderate, it's good for the environment anyway.
  • Multi-part Multi-part is when an email offers both an html and a text version of the same content. In most modern emailing toolsthe text version is automatically extracted from your html code. But this won't be the case everywhere. It's important that a text version is present, and that it contains content similar to the html version.

We'd like to end on a subject that's rarely mentioned, that of "template warmupThis is not a necessity in absolute terms. In absolute terms, it's not a necessity, but it's often reassuring for CRM teams who don't want to degrade their deliverability when a new template goes into production. The technique is relatively similar to that used to warm-up IP addresses or domain names. Start with small volumes, segment on responsive recipients, and gradually increase the volume.. But quite frankly, if you're ramping up a template, it'll be very quick. You can also warn your audience of the change (with the old look) so that they're reassured about the legitimacy of these emails.

Some tools and resources for deliverability and content

Tools to test the deliverability of your emails

Test the deliverability of an email can make sense. But beware, as this article clearly states, it's not the content of your email that will determine its deliverability, but your reputation and practices in the broadest sense. So don't hesitate to test the content of your emails, but keep in mind that the scope of this test will remain limited and will only reflect a small part of your performance.

Here are a few tools for testing the deliverability of email content:

  • Kickbox Email Spam Checker The test report will let you know if you're listed in a blocklist, and will give you information on a number of technical parameters (authentication, compliance with standards), as well as content-related elements such as the SpamAssassin score or the correct operation of links present in the email.
  • Scan My Email In the same vein, a French tool which, in addition to a battery of tests on IPs, domains, authentication and DNS configuration, also adds an Rspamd test to SpamAssassin.
  • Mail Tester This is one of the most widely used free tools for testing the deliverability of email content, but it should be used with caution. It relies mainly on SpamAssassin to function, in addition to a few criteria related to other content elements.
  • Litmus and EmailOnAcid Mainly known for their rendering test functions, which allow you to preview email display Litmus and EmailOnAcid can also be used in different email clients to submit an email to several anti-spam filters, and thus detect any deliverability incidents linked to the email content.
  • The deliverability monitoring solutions : There are many paid deliverability monitoring solutions on the market. These include many features that enable you to detect drops in deliverability performance and create automatic alerts when this happens. In most cases, these solutions also include ways of evaluating the content of your emails, even if this is not their main value. Here are a few solutions that Badsender is used to working with: Everest, Kickbox, GlockApps, Emailconsul, ...

Reliable" advice and information from deliverability specialists

Unfortunately, the internet is full of very unreliable content on the link between content and deliverability. Here are a few reliable sources

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The author
Picture of Jonathan Loriaux
Jonathan Loriaux
Active for more than ten years in emailing, my career path started on the technical side (integration of emailing campaigns) before turning to sales (as an eCRM expert) and finally to marketing consulting. For 9 years I have been the author of the blog Badsender.com. Emailing is not only an expertise, it really became my passion, that's why Badsender is now my main activity with the creation of an emailing consultant activity linked to the website.
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