This is a couple of solutions to the windows XP search bug.
I call it a bug, MS calls it a feature. If windows does not recognize the file extension it will be excluded from searches.
This cost businesses money in pointless searches for files that really do exist but claim not to.
It the banking world it is common to have transfer files with a sequential number extension (possibly a serialized date).
Trying to prove that your app is not skipping messages is far more difficult than it needs to be.