Originally Posted by
future elite
The T+ tickets work for all metro stops(Zones 1 + 2) but only Zone 1 for RER. I've been to one Zone 2 RER stop that let you have a free exit, but that may be an exception and not the norm.
Indeed, there is the well-known case of La Défense : it's in zone 2 and you can go via either Metro line 1 or RER A. A T+ ticket shall be valid only from travelling to there on line 1 and you would be blocked at the turnstile located at the RER exit.