1
Hi,
Unregistred users can't view pm and they redirect to 404 error page, this is because they redirect to user.php at pm folder not at root folder, so you can fix it as following:
edit modules/pm/viewpmsg.php and change line 32 from:
redirect_header("user.php",2,$errormessage);
To
redirect_header("../../user.php",2,$errormessage);