We present optical photometry and spectroscopy of the optical transient SN 2011A .
Our data spans 140 days after discovery including BVRIu ^ { \prime } g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } photometry and 11 epochs of optical spectroscopy .
Originally classified as a type IIn supernova ( SN IIn ) due to the presence of narrow H \alpha emission , this object shows exceptional characteristics .
Firstly , the light curve shows a double plateau ; a property only observed before in the impostor SN 1997bs .
Secondly , SN 2011A has a very low luminosity ( M _ { V } = -15.72 ) , placing it between normal luminous SNe IIn and SN impostors .
Thirdly , SN 2011A shows low velocity and high equivalent width absorption close to the sodium doublet , which increases with time and is most likely of circumstellar origin .
This evolution is also accompanied by a change of line profile ; when the absorption becomes stronger , a P–Cygni profile appears .
We discuss SN 2011A in the context of interacting SNe IIn and SN impostors , which appears to confirm the uniqueness of this transient .
While we favour an impostor origin for SN 2011A , we highlight the difficulty in differentiating between terminal and non–terminal interacting transients .