If you edit the Universal Email Server Behavior and open the Attachments window, make sure to select Server File Name from the Upload Files Biding and if the files are not stored at the root of the site, make sure to append the directory. for example if the files are at the root you will have something like this:
<?php echo $WA_DFP_UploadStatus["WA_UploadResult1"]["serverFileName"]; ?>
and if you have them in a folder, then the path should be updated to something like this:
yourfolder/<?php echo $WA_DFP_UploadStatus["WA_UploadResult1"]["serverFileName"]; ?>
let me know if you still have any other question.