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It's the same as banning gmail.com if some user sent a SPAM mail.Very many sites get blocked because of the actions of their users.
A quick websearch found this:-
(http://www.419scam.org/419-cabanova-com.htm)
I don't know anything about how Facebook works, but that's enough to have you in some email blocklists for some time.\
> I know there are probably many support requests but this is unacceptable behavior.
No. It is frustrating for you, but it is not unacceptable. They've had malware / spam / phishing coming from your domain. They've blocked your domain. That's good behaviour.