I was wondering if anyone else has seen this issue. A couple of weeks ago, I renamed my SQL Agent Operator account on many machines (SQL 2005, 2008, 2008R2 and 2012 machines) and from that point on, the SQL Agent stopped sending out notifications from JOBS, maintenance plan reports, etc.
FYI, I did the rename via right click rename, not T-SQL.
I deleted that Operator, created new one (same name) and re associated all Jobs and maintenance plans and all is working fine now.
aka Robert M Bishop
"Do or do not, there is no try" -- Yoda