Note: This is not a PBeM group, but you might like it, anyway; we're discussing the "pen-and-paper" Marvel Universe Roleplaying Game.

From the back cover:

SPIDER-MAN, THE X-MEN, DAREDEVIL, THE HULK
and the rest of the Marvel Universe come to life in this
revolutionary new roleplaying game from Marvel Comics.

Easier and more accessible than any RPG before, the Marvel Universe Roleplaying Game lets you play more than 40 of your favorite super heroes and super villains or create new heroes and villains of your own.