Well, I´m not a lawyer...but still I think its save to say it depends on what your contract with the mx provider and the CAMO orgaization says. Is the mx provider also the CAMO provider?
The way I see it, the CAMO is foremost responsible when it comes to ordering maintenance and AD´s.
But before 'going legal' I´d have an open word with them. That pays off in the long run IMO.