I have used two year old 2C-T-21 and 1 1/2 year old 2C-I, 2C-E and 5-Meo/4-Aco-DMT in the past without a noticeable reduction in potency, all of which had been stored in capsules wrapped in tin foil and placed within a standard prescription bottle. I think, as with any chemical compound, that, with proper storage, RC's could last relatively indefinitely (this is my general feeling, though; I dont have links to direct empirical evidence for this).
IME, your 2C-E should be fine and, IF there has been a reduction in potency, it would not be very apparent unless the material had been exposed to excessive heat, light and agitation (handling) during the 3 years you've had it.
~ vaya