Although Tumblr’s microblogging service is well-known for its public sharing format that allows you to instantly reblog posts by other users, Tumblr understands that you need flexibility to share or not share information as desired. As a result, the site offers you several privacy features, including options to privately reply to certain types of messages from the Tumblr Inbox using Fan Mail and Ask tools.
Replying to Fan Mail Messages
Fan Mail is Tumblr’s blogger-to-blogger private messaging service. Only other Tumblr users who follow your blog for more than 48 hours can send you a message. When you reply back to a Fan Mail message, the response is only seen by the message sender. As a result, your response is never shown to other followers or the general public unless you copy the sender’s message and your reply and then post both to your public blog.
Replying to Ask Questions
By default, Tumblr's Ask box allows any logged-in user to send you a question. Tumblr also gives you the option to set up the box to permit anonymous questions from users who haven't logged in and non-Tumblr users visiting your blog. To reply to an Ask question message from a specific user privately, click the paper and pencil icon below the question in your Tumblr Inbox, type your reply and then select the “Answer Privately” option. Since anonymous questions don't link to a specific person, you can only reply publicly to them.