First, let me say that this is not possible. Skype considers people to be blocked contacts only if they are in the blocked contacts list. If the user is not there then it is not blocked.
But there is a trick we can use in order to accomplish something similar to blocking someone without blocking him. We will not receive calls or messages from the user but unfortunately we will be able to receive contact requests (as Jivanda mentioned in the comments).
Basically the idea is…
…to unblock the contact (if we have already blocked him) and to also delete him from our contacts list. Afterwards we will set our Skype settings in a way that does not allow people outside our contacts list to contact us and we are done.
Follow these steps:
- If you have blocked the user then unblock him. Sign in with Skype and from the menu go to Tools -> Options… -> Privacy -> Blocked contacts. Choose the user from the list and click the Unblock this person button.
- If you haven’t deleted this person from you contacts list – do it. Right click on him and click Remove from contacts.
- The user may still show in the tab with the recent conversations. This is not a problem and it does not mean that it is in your contacts list. But if you want you can also remove him from there by deleting your Skype chat history.
- And now all that’s left is to tell Skype to not allow people outside our contacts list to bother us. From the menu go to: Tools -> Options… -> Privacy. Set all options here to people in my Contact list only (as shown below) and save the changes.