Since the heyday of AOL’s cheery “You’ve got mail” greeting, e-mail has been central to the online experience for millions of people.

But Mark Zuckerberg, the chief executive of Facebook, says e-mail is showing its age.

In his view, e-mail is too slow, too formal and too cumbersome, especially for young people who have grown up using text messages and online chats.

On Monday, Mr. Zuckerberg introduced a new unified messaging system for Facebook that allows people to communicate with one another on the Web and on mobile phones regardless of whether they are using e-mail, text messages or online chat services.

“We don’t think a modern messaging system is going to be e-mail,” he said.

The new service, Facebook Messages, is a bold move by Facebook to expand from a social network into a full-fledged communications system. It could help the company chip away even more at Internet portals like Google, Yahoo, MSN and AOL, which have used e-mail as one of their main draws with consumers.