Ding-dong Hotmail’s dead.

Microsoft has officially transferred all Hotmail accounts to its newer system: Outlook. There’s no need for Hotmail users to worry, though; their address will still be @hotmail and they can still send and receive messages from that account. The look and feel of the old system, however, has changed.

"Starting today, Microsoft will begin to upgrade every Hotmail user to Outlook.com…," the company said in a statement. "The upgrade is seamless and instant for Hotmail customers; everything including their @hotmail.com email address, password, contacts, etc., will stay the same."

Outlook.com is also "designed to make it easy to send hundreds of photos and videos in a single message," it said.

The website's users grew to 60 million in just a six-month period during its preview, Business Insider wrote, partly because it allowed users to connect easily with Facebook, Twitter and LinkedIn.

Microsoft said in a blog post: “Today, we’re excited to announce that we’ve completed upgrading all Hotmail customers to Outlook.com. Coupled with the growing organic excitement for Outlook.com, this has pushed us to over 400 million active Outlook.com accounts, including 125 million that are accessing email, calendar and contacts on a mobile device using Exchange ActiveSync.”

Gigaom added that Hotmail users will now be able to use Outlook's new features, which include SkyDrive integration.

But this doesn’t mean everyone is thrilled with the upgrades. Outlook group product manager Dick Craddock addressed the changes:

“Of course, whenever a widely used consumer service makes any substantial change, there will always be some folks that don’t like it, and that shows up in the feedback, too. It’s gratifying in a sense because it means those customers loved the previous set of changes we made. With a communication service that is constantly evolving, we try to strike the right balance between bringing out major improvements and keeping true to what our customers love.”

Hotmail was launched in 1996 and was one of the first Web-based email services.