Tumblr has finally given its users instant messaging, but not everyone will get it at once.

The media microblogging website is kicking off its long awaited instant messaging feature by offering it to 1,500 users at random, with the hopes that the feature will go viral across the site.

Those who've contracted instant messaging will notice the symptoms of it in their dashboard, where there'll be a smiley balloon icon. Don't contact a doctor. Contact a friend and spread it!

"You'll receive the messaging feature when a friend who has it already messages you, passing it along," Tumblr says. "Everyone will receive messaging in a few weeks."

As more users contract Tumblr's instant messaging, the condition known as "fan mail" will gradually fade away from the site.

"Once you have messaging, you'll notice that fan mail has changed a bit," adds Tumblr. "Old fan mail conversations can keep kicking, but you'll need to use messaging for initiating outgoing gems."

Tumblr is taking its time with the delivery of instant messaging, as the tool is still a work in progress and the site wants to install several other features to it over time. The company is currently working to support group chats, GIFs and images.

While some may sigh at the sight of another messaging tool, Tumblr apparently understands its user base — throngs of the creative type — and knows that they often invent whole new identities when using the site, according to David Karp, CEO and founder of Tumblr.

"They don't want to put their email address up, and they don't want to set up a second Snapchat account or, god forbid, link anybody to their Facebook," Karp says.

Some users are inventing entirely new brands and some are just kids who are finding their voice, adds Karp.

He goes on to say that Tumblr's instant messaging is really aimed at creative types who want to share common interests with other people around the world even if they don't know each other personally. Though typing text and sharing links to Tumblr posts may sound simple, Tumblr expects to see some complex creativity blossom out of it.