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).
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.
If you have ignored more than 25 accounts, you may need to click the "Next" button at the end of the list of usernames to see earlier ignored users.
Blocking a user that you follow also unfollows the account so that you no longer see the user's posts on your dashboard. If you want to see a user's posts on your dashboard again after unblocking the account, you must re-follow the user by visiting the blog and clicking the "Follow" button.
When you block an anonymous user in your Ask box, Tumblr blocks the user's IP address from sending you any more messages. However, Tumblr doesn't provide a way to unblock anonymous IP addresses at the time of publication.
You can manage your ignored users only on Tumblr's Web interface; the feature is inaccessible on mobile Tumblr apps.