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I've got a kid who's getting ready for his freshman year of high school. After I stopped feeling old, I reflected on that experience a bit: The cliques, the competition, the struggle to define your identity, and the teachers you believe are out to make your life miserable.

The more things change, the more things stay the same. High school kids still get stereotyped as jocks, nerds, rebels, goody-two-shoes, and outcasts. Humans love to put labels on everything, right?

So, if you can't beat 'em, join 'em. Let's slap some labels on our favorite email clients and mailbox providers and imagine what they'd be like if they attended Inbox High together and we were the vice principals.

The Breakfast Club of email clients

Have you ever watched The Breakfast Club and sympathized a little with Vice Principal Vernon? (No? Just me?). After all, he had to show up for detention on Saturday too, and what'd he do wrong?

Dealing with email client rendering issues has got to be almost as annoying as babysitting unruly teens with raging hormones. And just like Breakfast Clubbers Brian, Bender, Andrew, Allison, and Claire - each email client has idiosyncrasies you must take into account before you hit send.

Here's where we think major mailbox providers and email clients would land if they were one of the typical high school stereotypes.

Gmail: The Jock

Every high school has that over-achieving, multi-sport athlete who is good at just about everything. They even get pretty good grades – although we all know the teachers go easier on the kids who are good at sports.

Like jocks, Gmail has some skills that other email clients don’t. For instance, AMP emails allow you to bring interactivity to Gmail inboxes, but not many other email clients support the framework yet. Jocks also tend to throw their weight around a little. Like for instance, how Gmail led the way in implementing new rules for bulk senders if they want to avoid the spam folder.

Getting your message clipped in Gmail is the email geek equivalent of a getting a wedgie or a swirly from a high school jock.

Of course, there’s also the “dumb jock” stereotype, and sometimes Gmail seems to fit that too. Like why is it that a Google service like Gmail doesn’t support Google web fonts? And why does Gmail cause so many dark mode email development challenges?

From the email developer's perspective, there’s no ignoring Gmail. Without a doubt, a significant portion of your subscribers are using this email client regularly, So, that means finding ways to deal with problems like message clipping and hyperlink colors.

Check out these articles:

• Developing HTML Emails for Gmail: 14 Tips for Coding
• Gmail Email Clipping | How Developers Can Avoid It
• AMP Emails vs. HTML: What Gets Higher Conversion Rates?

Apple Mail: The Popular Girl

If people were voting for the prom queen of email clients, it would have to be Apple Mail. Thanks in part to the popularity of iPhones, there are a ton of people using Apple Mail to view their emails. But how popular is it?

According to an article on Apple Mail demographics from Sinch Mailjet, it could be as much as 54% of the contacts on your list. Kate Nowrouzi is VP of Deliverability and Product Strategy at Sinch Mailgun. She says that, among Mailgun’s users, more than one-third of opens were occurring on Apple Mail.

Speaking of open rates, like any self-respecting popular girl, Apple Mail cares a lot about respecting privacy.

“Tracking pixels? Eww… as if!”

~ Apple Mail

The arrival of Apple Mail Privacy Protection (AMPP) threw many email marketers for a loop. But AMPP didn’t mean the death of email. We all found ways to adjust, and stronger privacy protection is better for everyone.

The nicest thing about Apple Mail is that it offers more support for HTML and CSS features. The website Can I Email places it at the top of its Email Client Support Scoreboard. No wonder everyone loves it.

Check out these articles:

• Find Out if Your Subscribers Use Apple Mail Privacy Protection
• 7 Tips for Designing and Developing Emails for the iPhone
• How to Use Media Queries in HTML Emails

Outlook: The Troublemaker

Shouldn't a Microsoft product like Outlook be considered a nerd and not troublemaker? Obviously, you can be a little of both. Go ahead and ask any email developer you meet. The Outlook email client causes just as many headaches for email devs as Ferris Bueler did for his school principal.

It’s probably safe to say that at least 80% of the time when someone asks why you have to go out of your way to code something in an email, it’s because of Outlook. You’ll find it all the way at the bottom of Can I Email’s scoreboard of email clients. As of this writing, Outlook for Windows (the desktop versions) only supports 52 of the 219 CSS and HTML features that Can I Email is tracking.

For example, the main reason email developers use tables for layout is thanks to Outlook. Concerns around using GIFs in email marketing can also be blamed on Outlook. Many issues with blocked images and padding/spacing can be traced back to Outlook as well. However, Outlook inboxes are home to many B2B subscribers. Plus, anyone who still uses a Hotmail address (they do exist) is viewing their emails in Outlook, too. 

But here's the thing... Like the classic high school movie trope where the nerd is actually cool, the plain girl is actually beautiful, Outlook may go through a transformation. A new Outlook for Windows could mean the end of all those troubles the Word rendering engine has caused.

So, like a high school troublemaker with hidden potential, you just keep working with Outlook and believe the wayward email client changes its ways someday.

Check out these articles:

• Outlook HTML Emails: How to Fix 11 Common Rendering Issues
• How to use GIFS and GIF Fallbacks for Outlook Emails
• How to Create Excellent Emails for Outlook.com

Yahoo Mail and AOL Mail: The Hipster and the Trendsetter

Hipsters take pride in their appreciation for things that are outside of the mainstream. They liked that band/movie/style everyone likes now before it was cool.

Back in the ‘90s, AOL Mail was the biggest email provider in the world. It had 9 million users in 1997. Today, there are around 4 billion people using email across the globe. For those of you keeping track at home, 9 million is 0.00225% of 4 billion. 

Still, you have to give AOL credit for its role in email history. People got hooked on their inboxes thanks in part to that irresistible “You’ve got mail!” notification.

Also in the ‘90s, Yahoo! saw the rise of webmail coming and acquired RocketMail, which was one of two of the world’s first free webmail services. There’s no denying Yahoo! was an internet pioneer, and its email service was a big part of that. But sometimes pioneers die of dysentery along the Oregon Trail.

Yahoo Mail may not have the same size user base as the big three email clients (Gmail, Apple Mail, and Outlook). But it's a been somewhat of a trendsetter. Yahoo was right there with Gmail introducing new rules for email senders in 2024. It also supports AMP for Email, which is good news for those who love coding interactive emails.

While AOL and Yahoo Mail aren’t the most popular kids in school anymore, email marketers and developers still need to keep them in mind. There are still 1.5 million people paying for an AOL subscription. And Yahoo Mail still has well over 225 million users.

It’s unlikely that subscribers using these email clients make up a very large portion of your list. But if you strive for email perfection, you should keep an eye on how campaigns render in these mailbox providers too.

Other email client characters

Even smaller email clients could represent other stereotypical characters in a teen comedy.

For example, it’s easy to picture Thunderbird as the classic nerd archetype. It’s an open source email client that Mozilla developed to pair with its Firefox browser. Mozilla stopped supporting it in 2014, but the community kept it alive, updating the software and making donations. It’s since become part of a subsidiary of the Mozilla Foundation. We love it when the nerds win in the end. There are still around 25 million people using the Thunderbird email client.

Samsung Email is like the quiet shy kid nobody notices at first. It works a lot like Apple Mail in that users can get messages from different mailbox providers and email addresses in one place. It obviously comes pre-installed on Samsung phones and has some features that its users really like, including a simple and intuitive UI. 

Then, assuming this is an American teen comedy, there are a handful of email clients that are like quirky foreign exchange students.

• Web.de is Germany’s top email client with 17 million customers.
• Free.fr is a French telecommunications company with a popular webmail app.
• Libero.it provides an Italian webmail service with around 11 million users.

Of course, the big three email clients (Gmail, Apple Mail, Outlook) are also very popular in regions besides North America. But if you’re developing emails in Europe or for a global company, it’s smart to pay attention to these smaller email clients as well.

The final exam for email clients

We realize comparing your work in email marketing to a cranky high school principal isn’t exactly flattering. But try to think of yourself more like Mr. Belding from Saved by the Bell. He always wanted what was best for the kids. Or maybe you’re more like Dumbledore, trying to get a bunch of young Hogwarts students under control.

At some point, you’ve got to put these email clients to the test. That’s where an automated pre-send platform like Sinch Email on Acid is an excellent solution. With email testing, you can preview your campaigns on the most popular clients and devices.

Using Email on Acid is like having the best hall monitor in history. You’ve got someone keeping an eye out for issues so you can prevent those troublesome email clients from rendering your campaigns the wrong way. 

Sinch Email on Acid also helps you optimize for inbox display, accessibility, and deliverability. Take advantage of the free trial and see how it works today!