Facebook announced it would offer @facebook.com e-mail addresses to its 500m members, as it unveiled a major expansion into messaging systems.

The upgrade to Facebook’s Messages service will put it in competition with browser-based e-mail services from Microsoft, Yahoo and Google and open up its service and users to e-mail from outside Facebook.

Mark Zuckerberg, Facebook’s founder, told a news conference in San Francisco on Monday that the idea was to combine e-mail with instant messaging, texting and conversations in a seamless way, with e-mail becoming less important over time. “It will always be a part [of messaging] and maybe it can help push the way people do messaging more towards this kind of seamless, simple, real-time, immediate personal experience; that’s what we’re trying to do,” he said.