When you ignore an account on the Tumblr website, you remove the user from your Follow list and block your posts from appearing on the user's dashboard. Tumblr doesn't send you any private messages or dashboard notifications from the user. You ignore a user by entering the username in your Ignored Users list or by hovering over the username on your dashboard or in your Ask box, clicking the silhouette icon and selecting "Ignore" from the drop-down menu. The only way to unblock a Tumblr user is by unignoring the username in your Ignored Users list.
Log in to your Tumblr account and go to your Ignored Users dashboard (link in Resources).
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Locate the username of the user you want to unblock. Tumblr lists the users you've ignored in chronological order by when you ignored their accounts.
Click the "Stop Ignoring" button next to the username of the account you want to unblock. Tumblr immediately unblocks the username from your account.