Spam & other problems

I've been trying to configure Smartlist and have got a mixed bag of problems... I'm trying to create a private list, so have developed an accept list which is an exact duplicate of the dist list. However, some messages not being received by everyone on the dist list. And it appear some users on the accept list are unable to reply or post. And, to make matters worse, some of my users are receiving spam. Can anyone help with thise problems? Thanks, Sue Bott