Have you drilled down to the various alert options under the E-Alert tool?
https://public.govdelivery.com/accounts/PGCPS/subscriber/new
I found a reference to a PGCPS listserv by searching on the PGCPS website. Unfortunately, that document was dated from 2008 and I could not find a listserv. My school PTA uses a listserv which I know many other schools do, but I can't find anything @ the PGCPS level except for the E-Alert option.