by raul.san@sent.com:

When you create a file encoded to gob, it's very possible that the command
"file" misdetects it (like if it were known format).

The solution is add the header [3]byte{'g', 'o', 'b'} (it's tested and it works).

To avoid this problem, gob.NewEncoder could have an argument to insert an header, and
gob.NewDecoder to skip it.