to extract "From: " address properly

I am using a recipe to catch the email address in "From: " line to build a "white list", with this to extract the address: FROM=`formail -zX From: | formail -c -rt -xTo:` or FROM=`formail -zX From: | formail -zrx To:` or FROM=`formail -rtzxTo:` it works fine for some of the time, but once a while it ends up with a "foo@bar". I wonder why... (is it sometimes the top of the "From " line?) Zhiliang