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

Go to your 收件箱 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 潮流粉丝俱乐部 mobile site, then 你 should go to your mailbox using the 网址 with a tag /messages/trash 你 can find all of the messages sent to 你 由 your friend right there, amongst your trash mail. All 你 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 收件箱 instead of trash. Hope it helps. It works for Android 6.0 或者 higher. I'm not sure about the other mobile OS's though. 你 forgot to mention what kind of a mobile OS do 你 actually use, if you're using the 潮流粉丝俱乐部 mobile site in the first place. 你 should be 更多 specific in the future when it comes to 更多 detailed informations, so that we can all provide 你 with an adequate & satisfactory answer 你 deserve.