It is IMPOSSIBLE to find out who has blocked you. Why? well back in the day (MSN Messenger 7.0) there was a bug with a protocol that allowed people to be able to check if a user was online with/without their permission.

This ofcourse was Invasion of Privacy and it was quickly patched and it was fixed. Hence their is absolutely positively no way to know if a contact has you blocked. If you really must know, Make a second email. But I highly suggest you don't you might just aggrevate the person more.

However, Websites do sometimes say they can "SEE" who has blocked you, these websites are phishing/marketing scam sites. They will steal your identity and copy all your contacts so that they may spam them and sell their emails to the highest bidder.
I think Jason is right .

Anyway, msgdiscovery is a very nice tool for msn

Offcourse, there are some "tricks", like sending request from some different accs, or asking friend who also have friendship if he/she was online.