What do you do about group member's emails getting tagged as spam?

A couple of the members in our group have had their emails held up by the spam blocker even though they were legitimate emails. I went through the emails and can't find anything that looks like it might be targeted by a spam blocker! As the group moderator I didn't really want to have to check the spam folder everyday to release legitimate stuff. Our group is unlisted and by invite only...can I turn off the spam blocker? Other suggestions? Thanks!!!