I previously published “Things I’ve learned about sending email”. A lot of people seemed to like the post and thought it was a great intro to sending email or quick cheat sheet.

Some people followed up with me and wanted to know more about the building and testing process when it comes to HTML email. Here’s a brain dump of what I’ve learned about building and coding HTML emails.

Sidenote: If it's HTML Email Templates you're looking for, I've put together a bundle of fully responsive templates for startups, developers and marketers. Includes notifications, a monthly newsletter, a welcome email and more. Visit HTMLemail.io to preview and download them.

Email clients and rendering engines

Email clients use different rendering engines to render HTML emails:

Apple Mail, Outlook for Mac, Android Mail and iOS Mail use WebKit

Outlook 2000/02/03 use Internet Explorer

Outlook 2007/10/13 use Microsoft Word (yes, Word!)

(yes, Word!) Web clients use their browser’s respective engine e.g. Safari uses WebKit, Chrome uses Blink

Gmail strips out <link> tags and any CSS in the <style> tags, and any other CSS that isn’t inlined. Not just Gmail web but also the native Gmail mobile apps.

Update November 2016: Just recently Google announced support for embedded CSS and media queries in Gmail. This is HUGE for the email development industry. Now, as of September 2016, Gmail will support a slew of CSS properties which makes template development a lot easier for Gmail.

Remember clients will also add their own flavor of styles on top of yours e.g. Gmail sets all <td> fonts to font-family: arial,sans-serif; .

Litmus has a handy website dedicated to the current email client market share, based on their own internal stats (~1 billion emails).

As of April 2015 the top 5 looks like so:

Apple iPhone 28% Gmail 16% Apple iPad 11% Outlook 8% Apple Mail 8%

Of course you should look at your own stats to know which clients you need to focus on for your recipients.

MIME Multi-part and plain text

When you send an email it’s important to send both plain text and HTML. You do this by sending your email as multi-part MIME. Even in a world where you think every one uses clients that render HTML, you should still send plain text.

Most ESPs will construct the MIME for you so you don’t really need to worry about it. Some will also create a plain text version for you based on your HTML version.

Note that with the recent launch of Apple Watch, a new MIME part has surfaced: text/watch-html . This content will only be displayed in the Apple Watch (and any other clients that support this MIME type going forward).

Use tables not divs

Divs have positioning and box model issues in different clients, in particular those that use Microsoft Word (Outlook) to render. You can use divs if you want but safer to code like it’s 1999 and stick to tables.

Tables instead of divs

#ffffff instead of #fff

Padding instead of margins

CSS2 instead of CSS3

HTML4 instead of HTML5

background-color instead of background

HTML attributes instead of CSS

Inline CSS instead of stylesheets

These approaches are recommended best practices. You can certainly ignore the safe route and go above and beyond.

When using tables don’t forget border="0" cellpadding="0" cellspacing="0" . If you’re using Premailer it has special CSS declarations for applying these HTML attributes.

Inline CSS

Some clients will strip any CSS that isn’t inlined. You have a couple of options here:

Write CSS inline as you go

Use a web-based CSS inliner

CSS inliner Use a programmatic CSS inliner

CSS inliner Let your ESP (Email Service Provider) handle the inlining for you (if they support it)

Writing inline as you go isn’t exactly a scalable or maintainable solution so I tend not to, but I know a lot of email builders prefer it this way to maintain 100% control. If you do write your CSS inline manually then I recommend making use of snippets and/or a templating language with partials and helpers. This will save you repeating yourself.

Web based inliners include Responsive Email CSS Inliner Campaign Monitor, Mailchimp and Zurb’s Ink.

For a programmatic inliner I typically use the Premailer gem, or another package based on it.

Sidenote: Check out my grunt email design workflow, which will inline your Sass, compress your images, send you a preview and automate a bunch more of useful stuff.

Conditional targeting

We can apply specific CSS styles and show/hide elements and content for different versions of Outlook.

This would target all Microsoft Word based versions of Outlook:

<!--[if mso]> <p>Only Microsoft Word based versions of Outlook would see this.</p> <![endif]-->

This would target all IE based versions of Outlook:

<!--[if (IE)]> <p>Only IE based versions of Outlook would see this.</p> <![endif]-->

We can also target specific version numbers of Outlook:

<!--[if mso 12]> <p>Only Outlook 2007 would see this.</p> <![endif]-->

More on conditional statements for Outlook.

We can target WebKit based clients with a media query like this:

.special-webkit-element { display : none ; } @media screen and ( -webkit-min-device-pixel-ratio : 0 ) { .special-webkit-element { display : block !important ; } }

More on media queries for WebKit.

Mobile, media queries and responsive solutions

With email opens on mobile around the 50% mark, it’s more important than ever to ensure your emails are accessible and usable on smaller devices.

There are various solutions for making emails responsive. One of which is using media queries. Media queries cannot be inlined, therefore your CSS should look something like this.

< style type = "text/css" > @media only screen and ( max-width : 480px ){ .container { padding : 5px !important ; } img { height : auto !important ; max-width : 100% !important ; } } </ style >

!important; is important here, for lack of a better word, as you will be overriding your inline styles.

Don’t forget to add this to the head of your email:

<meta name= "viewport" content= "width=device-width" />

Some clients will strip out any CSS that isn’t inlined, until recently Gmail mobile apps, therefore this responsive technique will not work for those clients. Other solutions exist that do work, and you can always go with a 100% fluid width layout or narrow fixed layout for all devices.

Here is ActionRocket’s approach to designing responsive emails.

Things you may want to alter for smaller devices include:

Font size

Columns

Padding

Hide or show elements

Anna Yeaman has a long list of media query in email support, Brian Graves has a great website listing responsive email resources and Campaign Monitor have a detailed responsive email design guide.

Sidenote: Mailgun has a set of simple transactional HTML email templates available for download that are responsive.

Bullet proof buttons

It’s painful trying to achieve the perfect cross client button. As mentioned above you should be using tables and table cells for everything. This includes buttons.

My preference is to use this solution. Instead of styling a button like this:

<a href= "#" class= "btn btn-primary" > Click Here </a>

I’ll write it like this:

<table border= "0" cellspacing= "0" cellpadding= "0" class= "btn btn-primary" > <tr> <td align= "center" valign= "top" > <a href= "#" > Click Here </a> </td> </tr> </table>

Then once my CSS is inlined it will look like this:

<table border= "0" cellspacing= "0" cellpadding= "0" style= "box-sizing: border-box; border-collapse: separate !important; mso-table-lspace: 0pt; mso-table-rspace: 0pt; width: auto; padding-bottom: 15px; margin-left: auto; margin-right: auto;" > <tr> <td align= "center" valign= "top" style= "box-sizing: border-box; vertical-align: top; mso-table-lspace: 0pt; mso-table-rspace: 0pt; border-radius: 5px; text-align: center; background: #1271db;" > <a href= "#" style= "box-sizing: border-box; color: #ffffff; text-decoration: none; border-radius: 5px; cursor: pointer; display: inline-block; font-size: 14px; font-weight: bold; text-transform: capitalize; background: #1271db; margin: 0; padding: 12px 25px; border: 1px solid #1271db;" > Click Here </a> </td> </tr> </table>

This is just one way of implementing buttons in emails. I prefer it as it’s simpler and doesn’t involve image assets or VML. Admittedly it doesn’t always look amazing in every client, but I can live with that.

If you need pixel perfection across all clients, Stig from Campaign Monitor created a handy bullet proof button tool.

Typography

In general it’s easier to stick with standard system fonts. That includes Helvetica, Arial etc.

However, we can use web fonts like Google fonts. You should put them behind a WebKit conditional media query otherwise Outlook will mess up your type e.g.

<style> @import url(http://fonts.googleapis.com/css?family=Pacifico) ; /* Type styles for all clients */ h1 { font-family : Helvetica , Arial , serif ; } /* Type styles for WebKit clients */ @media screen and ( -webkit-min-device-pixel-ratio : 0 ) { h1 { font-family : Pacifico , Helvetica , Arial , serif !important ; } } </style>

More on web fonts in email by ActionRocket.

Remember to include font-family, font-size and color on every <td> or you risk the client overwriting your carefully chosen type styles.

Images and videos

Assume images are off/blocked by default.

Outlook, AOL, Yahoo have images blocked by default

Apple Mail, iOS, Gmail have images turned on

Remember to include good alt text. That could either tell the user what the image says or just reference what it is e.g. company logo, photos that link to interesting things

You can also be creative with alt text for clients that have images turned off.

Remember to include a basic image reset for all images e.g.

<img src= "" alt= "" width= "" height= "" border= "0" style= "border:0; outline:none; text-decoration:none; display:block;" >

Animated gifs are supported in most clients. Outlook 2007-2013 does not support animated gifs. They fall back to the first frame.

Other than Jonah Hill screaming, animated gifs are really useful for feature announcements in emails.

Video is supported in iOS, Apple Mail, Outlook.com. You can use media queries to show/hide the video based on the client. More on email video support at Email on Acid.

Kevin Mandeville wrote this great tutorial on coding HTML5 video as a background in an email. Impressive stuff and worth a look.

Remember to compress your media assets and upload them to a CDN (Content Delivery Network e.g. Rackspace or AWS). Most ESPs will handle this for you.

SVG (Scalable Vector Graphics) have a lot of advantages when using them for the web. As you would expect, email support varies and they require a couple of fallback hacks/conditionals. I typically stay away from SVG in email.

Icon fonts, like Font Awesome, fall into the same bucket as web fonts (see above). WebKit clients may or may not support them.

For retina ready images, supply a large (2-3x) image and resize it. I’ll typically save a low quality image that has 2x dimensions, which seems to work well (more on that technique).

Keep in mind that for Outlook you should tell the image how wide it should be with a width attribute otherwise it may render the actual width of the image and break your email.

Forms

Support for form elements vary. Best to stay clear and link to an external form if you need one. Campaign Monitor has some advice on forms here.

Obviously it depends on what your objectives are. It is safer to stay away from forms but I have seen RebelMail and MixMax doing interesting things with forms for surveys and ecommerce with good fallback support.

What the heck is VML?

VML (Vector Markup Language) is supported by Outlook. I honestly never use it and try to design emails in a way that I can avoid thinking about it.

Vector Markup Language (VML) is obsolete in Internet Explorer 10 (quirks and 10 document modes). — Microsoft

VML is no longer supported in new versions of IE, although as long as Outlook 2007/10/13 are around you will see it used. Typically for background images.

Can I use CSS3 and HTML5?

Sort of. Be sure to keep progressive enhancement in mind when using these.

Recently I’ve switched to using HTML5 doctype but not other HTML5 elements.

CSS3 wise, like the web, if you include rounded corners, box shadows etc. they will drop back for clients that don’t support them. CSS animations, for example, are supported in WebKit clients. It all comes down to what the rendering engine is for each client.

How do I include Gmail actions in my subject line?

These are handy actions available for Gmail. You’ve probably seen them from the likes of GitHub for issues or Amazon for orders.

Adding the code is straight forward. You have two options:

JSON-LD Microdata

Getting white listed involves a few more steps. You can test Gmail actions with a @gmail.com address.

Don’t forget about preheader text

Some clients show extra descriptions next to or under the subject lines. These clients include iOS, Apple Mail, Outlook 2013, Gmail, AOL.

Clients will grab the first bit of text they find in your email body and add it here.

Make the most of this and add a hidden element to your body content that appears first. This text should be an extra incentive for the user to open your email. Hide the text like so:

<span style= "color: transparent; display: none !important; height: 0; max-height: 0; max-width: 0; opacity: 0; overflow: hidden; mso-hide: all; visibility: hidden; width: 0;" > Preheader text goes here </span>

Use this subject/preheader tool by Austin Woodall to preview your email subjects and preheaders.

How do I test my email before sending it?

I always use Litmus as well as emailing myself and checking it on 2 or 3 devices. Email on Acid seems like a good alternative.

Conclusion

Building HTML email is a lot like building a web page. 10 years ago.

Email clients haven’t been as progressive as web browsers in adopting new standards, while we users and companies haven’t adopted new email clients like we have web browsers. Add to that the rise of mobile, we’re left in this state where we have to support so many convoluted clients and versions.

You can keep it simple and design email with a “What’s the minimal amount of effort required to get the maximum effect” approach. You can provide a bunch of fallbacks or hacks to ensure your emails are “bulletproof” and look identical across all clients. Or you can go above and beyond and experiment with things like web fonts, SVG, animations, video and provide a supperior experience for those that support it. For more useful information from a marketers point of view, read this email marketing beginner guide.

What’d I miss? What advice would you add to this list for any one else reading?