Changed mail creation to seconds instead of nanoseconds to reduce mail size.
Fixed deserialization bug in ReceiverLookupDocument, this is now type-safe (thanks to the GSON unit tests how to do this).
Fixed handling when ReceiverLookupDocument could not be read from database. Improved some variable and class names. Changed unit tests to check for exact strings e.g. eq(receiverLookupDocument1JSON) instead of isA(String.class) to proof correctness of mail storage. Added new unit tests to increase code coverage.