Until WLM 2009, there was a list of blocked/allowed contacts somewhere in Tool > Options.
With 2011, this is gone (or seems to be). The question is, how do I unblock a contact I no longer have in my contact list?
Don't think you can... unless you re-add them to Messenger, then unblock them. Or start a conversation from the actions menu, and then try unblocking them.
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