Hello student,

Actually vimukta jati are basically known as denotified tribes, who come under criminal tribes act of 1871. There are about 110 million people belongs to the denotified tribes, nomadic (https://en.m.wikipedia.org/wiki/Nomadic_tribes_in_India) or semi-nomadic tribes in India.

In 2008 ,NCDNSNT announced that this vimukta jati e will be comes under St category.

So you can select St category for post office job or any other things. Also you can search about that in in in your caste certificate.