  Since its launch in 1999, the XMM-\textit{Newton} mission has compiled the
largest catalogue of serendipitous X-ray sources, with the 3XMM being the third
version of this catalogue. This is because of the combination of a large
effective area (5000 $\rm cm^2$ at 1 keV) and a wide field of view (30 arcmin).
The 3XMM-DR6 catalogue contains about 470,000 unique X-ray sources over an area
of 982 $\rm deg^2$. A significant fraction of these (100,178 sources) have
reliable optical, near/mid-IR counterparts in the SDSS, PANSTARRS, VIDEO,
UKIDSS and WISE surveys. In a previous paper we have presented photometric
redshifts for these sources using the TPZ machine learning algorithm. About one
fourth of these (22,677) have adequate photon statistics so that a reliable
X-ray spectrum can be extracted. Obviously, owing to both the X-ray counts
selection and the optical counterpart constraint, the sample above is biased
towards the bright sources. Here, we present XMMFITCAT-Z: a spectral fit
catalogue for these sources using the Bayesian X-ray Analysis (BXA) technique.
As a science demonstration of the potential of the present catalogue, we
comment on the optical and mid-IR colours of the 765 X-ray absorbed sources
with $N_\mathrm{H} > 10^{22}\,\mathrm{cm}^{-2}$. We show that a considerable
fraction of X-ray selected AGN would not be classified as AGN following the
mid-IR W1-W2 vs. W2 selection criterion. These are AGN with lower luminosities,
where the contribution of the host galaxy to the MIR emission is
non-negligible. Only one third of obscured AGN in X-rays present red colours or
r-W2 > 6. Then it appears that the r-W2 criterion, often used in the literature
for the selection of obscured AGN, produces very different X-ray absorbed AGN
samples compared to the standard X-ray selection criteria.
