Context : T Tau stars display different X-ray properties depending on whether they are accreting ( classical T Tau stars ; CTTS ) or not ( weak-line T Tau stars ; WTTS ) .
X-ray properties may provide insight into the accretion process between disk and stellar surface .

Aims : We use data from the XMM-Newton Extended Survey of the Taurus Molecular Cloud ( XEST ) to study differences in X-ray properties between CTTS and WTTS .

Methods : XEST data are used to perform correlation and regression analysis between X-ray parameters and stellar properties .

Results : We confirm the existence of a X-ray luminosity ( L _ { X } ) vs. mass ( M ) relation , L _ { X } \propto M ^ { 1.69 \pm 0.11 } , but this relation is a consequence of X-ray saturation and a mass vs. bolometric luminosity ( L _ { * } ) relation for the TTS with an average age of 2.4 Myr .
X-ray saturation indicates L _ { X } = { const } L _ { * } , although the constant is different for the two subsamples : const = 10 ^ { -3.73 \pm 0.05 } for CTTS and const = 10 ^ { -3.39 \pm 0.06 } for WTTS .
Given a similar L _ { * } distribution of both samples , the X-ray luminosity function also reflects a real X-ray deficiency in CTTS , by a factor of \approx 2 compared to WTTS .
The average electron temperatures T _ { av } are correlated with L _ { X } in WTTS but not in CTTS ; CTTS sources are on average hotter than WTTS sources .
At best marginal dependencies are found between X-ray properties and mass accretion rates or age .

Conclusions : The most fundamental properties are the two saturation laws , indicating suppressed L _ { X } for CTTS .
We speculate that some of the accreting material in CTTS is cooling active regions to temperatures that may not significantly emit in the X-ray band , and if they do , high-resolution spectroscopy may be required to identify lines formed in such plasma , while CCD cameras do not detect these components .
The similarity of the L _ { X } vs . T _ { av } dependencies in WTTS and main-sequence stars as well as their similar X-ray saturation laws suggests similar physical processes for the hot plasma , i.e. , heating and radiation of a magnetic corona .