Can somebody please tell me how can I un-block my friend to get his messages in my mailbox once again?

Go to your kotak masuk and select the Blocked Users section. There should be a green Unblock button to the right of your friend's username. Click on that button and you've unblocked him.

If you're on fanpop mobile site, then anda should go to your mailbox using the link with a tag /messages/trash anda can find all of the messages sent to anda oleh your friend right there, amongst your trash mail. All anda gotta do now is simply to choose your friend's message & tap Undelete selected messages button beneath the list. That's it. It's as simple as that! Your friend is now unblocked & all of his messages will go to your kotak masuk instead of trash. Hope it helps. It works for Android 6.0 atau higher. I'm not sure about the other mobile OS's though. anda forgot to mention what kind of a mobile OS do anda actually use, if you're using the fanpop mobile site in the first place. anda should be lebih specific in the future when it comes to lebih detailed informations, so that we can all provide anda with an adequate & satisfactory answer anda deserve.