After all, according to the text he was apparently left in Graendal's palace. We never heard that Forsaken like Sammael, Be'lal or Rahvin warded their belongings, so it seems doubtful that Graendal would (besides that there is no indication I know of in the books that she actually did it that). At the very least the messenger could e.g. check what pets Graendal got and that way report a bit about her possible plans to Moridin.