Jeffrey Bonforte, Yahoo's SVP of Communication Products, said the changes were timed to coincide with Yahoo Mail's 16th birthday and are intended to make the service not only more elegant but also more efficient. 

"Things you do all of the time like search, starring, and deleting are now one-click actions that appear when you hover over an email. We also wanted to give you more breathing room in your inbox, so you can collapse the left-hand toolbar to be more productive," Bonforte said in a posting on Yahoo's company blog.

As party favors, Yahoo is throwing in features previously reserved for Premium Mail Plus customers. Disposable email addresses, enhanced filters and automatic message forwarding are now available for everyone. Yahoo is also increasing storage to 1 terrabytes (TB), enough to last several lifetimes for just about any user. 

It's part of an effort by CEO Marissa Mayer to boost user engagement with Yahoo's products. Yahoo mail is an especially vital element, as it can serve as a gateway to other Yahoo services.  

There's also a big of window dressing in the new design. 

"We wanted to bring a little inspiration into your inbox — dress it up a bit if you will.  We’re doing that by introducing visually rich themes, including curated Flickr photos, for your browser, smartphone and tablet. Choose a new photo theme in one place, and it will apply across all your devices. After all, your inbox doesn’t have to be a plain white box with text dropped into it," Bonforte said.