I did already.

Okay, maybe some clarification: it's not apparent whether or not every dragonkin elf is immortal or not, but the general consensus seems to be on "not." It is suggested the dragons might have made a bargain with a Passion or two, or used dragon ritual magic, to enact the right changes, or at least hide the usual deformities.
As far as "binding" goes-there is no evidence that the Great Dragons magically bound the elves to them. Ever. There is anecdotal evidence that the Great Dragons enslaved at least certain of the IEs, however, which might or might not have included magical binding, but no evidence of such binding still exists.
As far as other races go, there's evidence that dragons can significantly lengthen lifespans but not render complete immortality. The Denairastas Clan of Iopos is led by a very long-lived human, but his supplements his dragonkin blood with Nethermancy. The Kings of Throal benefited from three potions provided by the Great Dragons that extended their lifespans. The t'skrang of the Serpent River were taught how to enter a magical hibernation (possibly similar to that of the dragons themselves), which allowed them to live out the Scourge. There is one account of a human that was transformed to be able to take on a drake's form and gain a significantly expanded lifespan, but even drakes are mortal.