I was reading "The Grand History of Eberron" and I came across this passage in the race section (Warforged, page 432):
The editor was using source material and novels, though it appears to have been sourced from 2006. Things could have changed since then. Does anyone know if there is a lore appropriate reason to ALLOW WF to take the undead forms available to PM's?The Treaty of Thronehold gave warforged their freedom, but only after great debate. House Cannith and Thrane argued ardently that warforged were not living creatures because they do not possess souls. Their evidence for this was that warforged cannot become undead by any known method, not even ghosts or wraiths. They are immune to energy drain, and no one knows of a warforged soul in Dolurrh, the Realm of the Dead. Breland argued that because warforged can be raised from the dead, they must have souls. Of course, House Cannith and Thrane countered that no warforged brought back from death told tales of any kind of afterlife. In the end, the Question of Souls, as that portion of the negotiations came to be known, was left unanswered.