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Constraining the population of intermediate black holes (IMBHs) can help solveone of the long-standing problems in modern astrophysics the origin ofsupermassive black holes (SMBHs). Among the 305 optically selected IMBHcandidates (3e4 and amp lt MBH and amp lt 2e5 MSun) published to date which reside in galaxy centersand appear as weak type-I AGN only 24 are confirmed in X-rays and 23 more areawaiting confirmation with Chandra. We propose an XMM-Newton fulfil program for40 IMBH candidates to probe lower Eddington rates and BHs residing in non-dwarfhost galaxies. Our program will help to understand the masses of seed blackholes in the early Universe. [truncated! Please see actual data for full text]