  The connection between X-ray weakness and powerful X-ray outflows is both
expected in a scenario where outflows are connected with radiation-driven
winds, and observed in several sources, both in the local Universe and at high
redshift. Here I present the first results of a new study of this possible
connection based on a search for SDSS quasars with weak X-ray emission in
serendipitous XMM-Newton observations. The selected objects have a "normal"
optical/UV blue continuum, but a flat and extraordinarily weak X-ray spectrum.
The availability of rest-frame optical/UV spectra allows to check for the
signature of outflows in the absorption lines and/or in the profiles of the
emission lines. This method could reveal the presence of a population of so-far
overlooked outflowing quasars and confirm the connection between winds and
X-ray weakness in quasars.
