Perhaps the best Gmail feature that Google has been testing for years is one you might not even know exists: Undo Send. It delays sending your email for a few seconds after you click Send, so you can take it back if you, for example, spell someone's name wrong.

After the feature spent six years in public beta, Google announced in a blog post this week that Undo Send is becoming an official setting.

For users who already had the Undo Send beta enabled, the feature will remain on, and those who didn't can turn it on via the General tab under Settings.

When it launched in 2009, Undo Send would delay sending your emails for five seconds, but it now lets users choose if they want to hold their mail for 5, 10, 20 or 30 seconds.

Google Labs is a collection of Gmail features that allows users to opt in to public betas for services that aren't quite yet ready for prime time. Undo Send was one of the most popular of the Labs features.

However, Undo Send is not currently available on mobile, so you're out of luck if you want to retract an email you sent via your phone. But there's good news: Google said it will roll out the feature to mobile in the future but didn't elaborate on the timeline.

Google has not yet responded to a Mashable request for comment as to why it took so long for Undo Send to move up from Google Labs, where it was undergoing testing. Of course, Gmail itself was in beta for five years from 2004 to 2009, so the company is no stranger to long test periods.

If you don't already have this feature turned on, it might just save you from that next embarrassing typo.