Dear Prestigious Literary Market,
I want to sincerely apologize for sending you the same story twice. Does it help that this version has been revised and polished? I highly doubt it. Do I need to explain the details of how my supposedly-meticulous submissions-tracking system failed me? Surely not.
All I can do to improve matters at this point is NOT email with an apology, thereby adding to your already overflowing inbox.
Thank you for understanding,