Thank you for the link to mireth.com. Within mireth I found this page which is exactly what I want to do and may do the trick:
http://www.mireth.com/wt/nxme-erase-email-trash.html
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++How to erase email instead of deleting email++
++using NetShred X++
+Mac OS X Internet Track Eraser+
+When you delete an email or move it to the trash, it's not really gone and can be recovered. You can use NetShred X to ERASE email so it can't be recovered.+
+* NetShred X can erase email that's in the mail trash bin. If the mail trash bin has been emptied, NetShred X can't erase the email. To erase these emails you've previously deleted, see notes+
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