I would like to start off by thanking the Shiachat community for their sincerity. The anonymous nature of the internet is sometimes a great luxury. It is questions like these that I do not think that I would get a sincere response to in real life.
My question to my Shia siblings: What is the ruling on one that does not believe in the Imams?
Before responding, I want you to remember that I do not want your personal opinion, but I want proper evidences.
There is a link that full with these kind of quotations.
Baqir Majlisi declared in Biharul Anwar, Volume 23 Page 290 (Published in Beirut): "Note that the terms shirk (polytheism) and kufr (disbelief) apply to one who does not believe in the Imamah of Ali (as) or his progeny, and gives precedence to others over them, proving that they are kuffar destined to reside in hell."
Allama Abdullah al Mamqani wrote in Tanqihul Maqal