Called Priority Inbox, the feature will be released with the beta, or test, label and is being described for now as "experimental" by the company.
All individual Gmail users will gain access to it in the coming days. Availability for people who use it as part of Google Apps will depend on whether domain administrators allow their users to activate "pre-release" features.
The motivation behind Priority Inbox is Google's conviction that the problem of email overload continues getting worse, forcing people to spend much time and effort managing their inbox both for personal and work-related matters.
Priority Inbox is an additional, optional view of inbox messages. People who choose it can toggle back to other more conventional views, such as listing messages chronologically by arrival timestamp or alphabetically by the senders' names or subject lines.
"Gmail's Priority Inbox is part of a broader trend to help users cope with email overload and promote inbox efficiency," said Gartner analyst Matt Cain via email. "There is a thriving market for Outlook plug-ins that help users winnow large volumes of mail."
Those include tools from Xobni and ClearContext, while Microsoft itself has added inbox-efficiency features in Outlook 2010, Cain said.
"The large consumer base of Gmail users, however, will give immediate and widespread exposure of this message triage approach, which will in turn spark demand for similar services in the enterprise," he added.
While many email programs let users set up filters and rules for their inboxes, the manual process can be complicated, so Google simplifies it by building the functionality into Gmail via automated algorithms, said Rebecca Wettemann, a Nucleus Research analyst. "Information overload continues to be a problem and this is a nice step to drive savings," she said via email.
"Unfortunately, we'll all still have to be on the lookout for emails that don't fit the patterns that can be important," Wettemann added.
With Priority Inbox activated, Gmail divides the inbox into three sections: the top one contains the most important and unread messages; the middle one has messages that have been flagged by users with a star to highlight them; and the last section has all other messages.
Matthew Glotzbach, director of product management in Google's Enterprise unit, sees Priority Inbox as a sort of inverted spam filter which, instead of blocking and setting aside unsolicited messages, prioritizes items in the inbox so that users can attend more quickly to the most important emails.
"If you're in meetings and you come back to your email and you have five minutes between appointments and you have 50 emails, which five messages do you spend your time on in that window of time?" Glotzbach said. Priority Inbox aims to automate that and simplify that decision, he said.
Priority Inbox's functionality is only partially available through third-party client software accessed via POP or IMAP like Outlook. With Priority Inbox activated, an icon appears next to important messages in the inbox of these email software programs, but the message list isn't rearranged, according to Google. "Priority Inbox works best when viewed in Gmail's web [user interface]," a Google spokesman said via email.
The algorithmic calculation that Gmail uses to assign priority includes a variety of parameters, including the frequency with which the user exchanges messages with different senders; the messages that get read and replied to, or, conversely, ignored; and manual indications from users ranking messages as more or less important.
Google provides a variety of options for users to manually customize Priority Inbox settings and preferences if they so choose.
Internal tests at Google showed that people who used Priority Inbox spent on average 6 percent less time managing email, or an entire work-week per year in the case of an employee who normally spends 13 hours per week on email.
"We see this as an ongoing evolution of the focus of Gmail, which has always been around addressing this problem of information overload," Glotzbach said.
Existing Gmail features intended to address this problem include the product's conversation view, which groups together email threads; the search feature, which indexes messages' full text; and its antispam technology.
If the 6 percent time-saving rate holds true for most users, Priority Inbox will be valuable because email will remain as the primary collaboration platform, despite the emergence of tools like shared documents that can be group-edited, said industry analyst Michael Osterman, president of Osterman Research.
"My only concern would be the algorithms that would identify content as important versus less important. This could lead to false positives in which important content is not identified properly," he said. "This is not a serious issue, since nothing will be deleted, but it could lead to delay in accessing important emails."