Email design: what counts is the opening environment of the recipients, not the distribution of the domain names!

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email design

I never liked the term 'mail client'. I don't find it clear at all. What exactly are we talking about when we talk about 'mail client'? I understand the term 'domain' and even 'destination' when I discuss deliverability with Jonathan or Sebastian. But when I talk design and integration with Grégory, Thomas, Fabien, they talk to me about mail client, webmail, email software, application, version, platform, email client...
And now, I'm completely smitten, it annoys me.

Here is an example of a conversation I can have internally:

"Greg, a customer tells me the email is broken on Outlook
- Ok, he opened it on which email client?
- Uh...The email was sent to an outlook address
- Yes, but he opened it with what application?
- What?!
- Ask him via which platform and version he opened his email. Without that information, I can't reproduce the bug.

People often say "Email is broken on Outlook". So stupidly, I thought that if the database was 30% of @outlook addresses, then 30% of the recipients would see the display bug.
I had it ALL WRONG.
After 14 years of experience in emailing, I finally understood why Gregory was asking me all those questions...

I'm sure I'm not the only one in this situation, so I'm sharing with you what I understood.

Recipient's domain = Mailbox Provider = ISP = destination = Example :

  • Possibility of grouping domains by destination (Example: the,, are grouped in the Microsoft destination)
  • Useful for deliverability because you can group deliverability statistics on a group of domains that use the same anti-spam infrastructure. For example, a soft bounce rate that explodes at Yahoo will indicate a potential delivery incident on,,, ...
  • Most routing tools offer statistics by domain name. However, they do not group all statistics by destination.

Opening environment = Mail client = Mail software = Webmail = Application = Example : Outlook 2016

  • The recipients of your database open their emails in an 'environment'. This environment is conditioned by several parameters.
    For example, Jean-Michel ( has an iPhone, he uses the Apple Mail application on it. In addition, he checks his emails on his computer with the Outlook 2016 software.
    Jean-Michel consults these emails via 2 different environments.
  • In fact, whatever the domain of the recipient's email address, the opening environment can be very different and can be characterized by :
    • The type of terminal used: computer, mobile, tablet
    • The operating system (especially on mobile): iOS, Android, Windows, Macos, Linux, ...
    • The application used, in its different versions (whether on computer or mobile) : Outlook 2016, Outlook 2013, Apple Mail, Tunderbird, Gmail App, Orange iOS, ...
    • The webmail used : Gmail, Yahoo!, Orange, Free, ...
    • The browser used to connect to the webmail: Chrome 90, Firefox 67, Safari 14.1, Microsoft Edge 44
  • Each environment combination has its own rules for displaying emails and understanding HTML. For example, Outlook apps for iOS and Android may not react the same way.
  • So if Badsender sends an email with a great carousel block, Jean-Michel will see the carousel if he views the email from his mobile and he will see the degradation (e.g., still images) if he/she is viewing the email from his/her computer.
  • As far as I know, the distribution stats by opening environment are rarely available in the routing tools.

Revelation of the day

So what matters is to know the distribution by email client and not by domain if we want to understand what is manageable in terms of HTML code, innovation in content, ...

And it is HYPER important in fact. Especially since there is no global trend. The statistics per opening environment depend a lot on the advertiser. It depends on the socio-professional category, the age range, the sector (BtoB / BtoC), etc.

We can very well have a destination distribution of the type :

But in fact, the breakdown of openings by environment is this:

  • 40% Apple Mail iPhone
  • 35% Gmail
  • 10% Apple Mail Mac
  • 5% Outlook
  • 10% Other

How to know the distribution of the openings?

Several possibilities:

  1. You already have these statistics in your sending tool. Great! Good for you.
  2. Alternatively, you can open an account on one of the following tools:,, Everest (fire
    You get opening tracking codes that you insert in your email campaigns.
    A few days later, you will get reports like this:
    And also other stats such as: time spent reading your emails, geolocation, top links clicked...
Example of a report on EmailOnAcid

If you are a Return Path customer, you must have access to the 250ok tool. So in that case, this is great for you!

Of course, Badsender can do this analysis for you 🙂

PS : @dear LePatronusers : please note that the opening tracking codes can be industrialized directly in our email builder LePatron. Great for a follow-up in time!

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