Very young open clusters are ideal places to study the X-ray properties of a homogeneous population of early-type stars. In this respect, the IC 1805 open cluster is very interesting as it hosts the O4 If+ star HD 15570 that is thought to be in an evolutionary stage intermediate between a normal O-star and a Wolf-Rayet star. Such a star could provide a test for theoretical models aiming at explaining the empirical scaling relation between the X-ray and bolometric luminosities of O-type stars. The authors have observed IC 1805 with XMM-Newton and further collected optical spectroscopy of some of the O-star members of the cluster. The optical spectra allowed them to revisit the orbital solutions of BD +60 497 and HD 15558, and provided the first evidence of binarity for BD +60 498. X-ray emission from colliding winds does not appear to play an important role among the O-stars of IC 1805. Notably, the X-ray fluxes do not vary significantly between archival X-ray observations and the present XMM-Newton pointing. The very fast rotator BD +60 513, and to a lesser extent the O4 If+ star HD 15570, appear somewhat underluminous. While the underluminosity of HD 15570 is only marginally significant, its amplitude is found to be compatible with theoretical expectations based on its stellar and wind properties. A number of other X-ray sources are detected in the field, and the brightest objects, many of which are likely low-mass pre-main sequence stars, are analyzed in detail. This table provides the full catalog of the 191 X-ray sources detected with the EPIC detectors onboard XMM-Newton in the direction of the IC 1805 cluster. The coordinates of the sources were cross-correlated with the optical and IR catalogs of Straizys et al. (2013, A&A, 554, A3), Wolff et al. (2011, ApJ, 726, 19), and the SIMBAD database. The authors adopted in each case a correlation radius of 4 arcseconds. This table was created by the HEASARC in October 2016 based on the electronic version of Table A1 from the reference paper which was obtained from the CDS (their catalog J/A+A/594/A82 file tablea1.dat). This is a service provided by NASA HEASARC .