Six plus weeks and no more mailings. It's pretty clear that EDF doesn't actually pull you from the mailing list the first time you ask, in some vain hope that sending you dead trees will get you to support them. If you're getting bombarded by paper mailings, call, get taken off the list, wait for six weeks, and if you're still seeing mailings, call again and be unequivocable.
And also, don't support Environmental Defense - there are plenty of better, often more local environmental groups that don't operate this way.
