Sending A Alert Message Using Send Mail Task

i have developed a pakage which populates a two different tables with reference to the xml files added to a folder which is watched by a security WMI task.it is governed by a sequence container which contains three for each loop container for working on the different files.i have different event handlers set up inside for each loop container tasks which contains , data flow task, execute sql task, and moving the processed file to the desired destination.i want to set up a send mail task on the package level using event handler on error, where i have set up a task for looging the error to the error table , i have tried to collect all the error messages in a array list variable . and trying to use that variable a s a message source. i could not under stand if i set the propogation variable in the sequence container as false than will the onpost execute event will fire the onpostexecute event handler in the package level.if show how can i send only one email for all the errors of package with error looging.