Yahoo Mail
Yahoo Mail is a free consumer email service. Initially launched in 1997, Yahoo Mail has a long history and enjoys great popularity. The web version of Yahoo Mail has undergone a number of service and interface updates over the years. The most recent version, released in October 2013, was the subject of much criticism from users.
Yahoo also provides a number of mobile apps for popular platforms like iOS, Android, and Windows Phone, along with support for integrating the Yahoo Mail platform into mobile and desktop clients via POP3 and IMAP.
Market Share
Yahoo Mail currently represents 6% of the email client market, placing it at #7 in our email client market share top ten. It should be noted that Yahoo Mail has experienced a steady decline in users. When we took a look at the email client landscape in June 2012, Yahoo boasted 13% market share. While Yahoo is still a very popular client, we predict a continued decrease in Yahoo webmail opens, as more and more users move to mobile clients for iOS and Android.
Deliverability
Yahoo Mail takes a similar approach to deliverability as other email services. It combines its own algorithms with user-provided spam reports to identify and block suspected spam messages. While many platforms emphasize third-party blacklists and ISP reports, Yahoo places a strong emphasis on checking the content of emails when determining whether or not a message is spam. Compliance with the CAN-SPAM Act of 2003 is strongly recommended, even for senders outside of the United States. A full breakdown of Yahoo’s sending guidelines can be found here.
Rendering
While the Yahoo Mail webmail client is subject to browser quirks, Yahoo Mail generally has very good support for the most common HTML and CSS used in email design today. The most notable omission is support for CSS positioning rules like top, right, bottom, and left.
Up until this past April, Yahoo Mail had two major problems with how it rendered email. It lacked support for media queries, leading to mobile styles being displayed on desktop, and it added a class of .yshortcuts to links which forced them to display links as blue. Both issues required unique hacks to get emails rendering correctly. Fortunately, Campaign Monitor reported that Yahoo has remedied both issues in the current version of Yahoo Mail’s web client. If you're still seeing blue links in Yahoo Mail, even when styled using inline CSS, you may want to try this fix.
Now, the most common problem designers will face is due to how modern web browsers interpret and display images. Images are, by default, inline elements. Most browsers take this into account when rendering images and force alignment with the baseline of surrounding text. Even when text isn’t present in the same table cell as images, this results in a gap underneath images in emails.
A quick fix for this is to declare images as block-level elements in the img tag:
<img src="..." height="..." width="..." border="..." alt="..." style="display: block;">
This helps images display properly not only in Yahoo Mail, but most webmail clients today.
Finally, Yahoo Mail does not have great support for CSS3 and HTML5. This includes the use of the canvas, audio, and video HTML5 tags as well as CSS3 properties like border-radius and box-shadow. Yahoo Mail does support text-shadow, though.
Table-Layout Fix
In mid-2014, Yahoo pushed an update to Mail that caused center-aligned tables to align to the left, regardless of the declared HTML attribute. A fix was quickly found in the Community that allows for aligned tables to be correctly positioned. The fix consists of adding the following to the outer-most container table in your email design:
style="table-layout: fixed;"
You can read more about the table-layout fix in this blog post on the Litmus blog.
References
Email Client Market Share
Wikipedia Yahoo Mail Article
Campaign Monitor's Guide to CSS Support
MailChimp's CSS Support Guide
Yahoo Anti-Spam
Media Query Issues in Yahoo Mail
Yahoo Best Practices for Bulk Senders
Yahoo Mail Listens and Fixes Bugs
Remove Gaps in Images