Gmail's already powerful search functionality received a small but significantly useful update today. As reported by the Google Operating System blog, the popular webmail service can now search inside more file types attached to messages. Previously, if someone sent you a text file or an HTML document, Gmail indexed its content, but it couldn't index other popular attachment formats.

Now Google is adding support for .pdf files, .doc documents, and .ppt presentations. Some old attachments may not be indexed yet but that will presumably change in the next few days and weeks. To search inside attachments simply add the prefix "has:attachment" before your search query. You can also limit queries to specific file types by typing "has:attachment filename:extension" into the search field – entering "has:attachment filename:pdf" and some keywords will restrict your search to PDF files, for example.

Gmail is one of the top three email services in the world but whether it has blown past Hotmail and Yahoo depends on who you ask. According to Google, the service counts more than 425 million monthly active users as of June 2012, up from 350 million in January. However, comScore puts the figure significantly lower at 289 million. The market research firm says Hotmail is still ranked first with a little over 324 million unique users in June, down 4% from last year, and Yahoo is second with a little over 290 million users in the same timeframe.