In September 2015, Tumblr changed how threads of comments on reblogged posts are displayed; rather than a nested view with indentations for each post, all reblogs are now shown in a flat view, and user avatars were also added.
The change was intended to improve the legibility of reblogs, especially on mobile platforms, and complements the inability to edit existing comments.
In addition, a reported 16.45% of blogs on Tumblr exclusively contain porn.
Tumblr also offered a "fan mail" function, allowing users to send messages to blogs that they follow.
On November 10, 2015, Tumblr introduced an integrated instant messaging function, allowing users to chat between other Tumblr users.
In July 2015, the system was modified so that users cannot remove or edit individual comments by other users when reblogging a post; existing comments can only be removed all at once.
Tumblr staff argued that the change was intended to combat "misattribution".
As no one had done so after a year of waiting, Karp and developer Marco Arment began working on their own tumblelogging platform.
In early June 2012, Tumblr featured its first major brand advertising campaign in conjunction with Adidas, who launched an official soccer Tumblr blog and bought placements on the user dashboard.
As addressed in these policies, we are constantly taking measures to ensure our users can avoid this content unless they'd like to see it.
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The feature is being rolled out in a "viral" manner; it was initially made available to a group of 1500 users; other users may receive access to the messaging system if they are sent a message by any user that has received access to the system itself.