Mailman

I am the administrator of a mailman listserv, and I have received
complaints from a handful of list members that they are not receiving my
listserv emails. I don't know if it's relevant that three of these four
members are aol users; the fourth is not. Does anyone know why certain
list members (and I don't know how many more there are) might not be
receiving mail? Additionally, I haven't received a single bounce-back
message since this other problem cropped up, despite knowing that there are
some wrong addresses on the list. Any advice that anyone has on either of
these perplexing issues would be appreciated.