Google announced today that you can now search for emails by file size in Gmail. To do so, you would enter queries in formats such as: "size:5m" or "larger:5m".
Gmail will also let you search for emails, based on when they were sent, in more flexible ways. You can do so by searching something like: "older_than:1y". Or you can do combinations:
"These changes go hand in hand with other recent enhancements to search such as the improved autocomplete predictions and a field trial for instant results from Gmail, Google Drive and more as you type," Google says in a blog post.
You can see a complete list of all Gmail search operators here.
Recent data from comScore indicates that Gmail is now the largest webmail service in the world (though it's still behind Yahoo in the U.S.). If a recent report is any indication, Yahoo is about to make a big competitive push against Google, with the help of its new CEO (and former Googler) Marissa Mayer.
Google has also made some search improvements to Google Drive.