I've seen this brought up before with 3.7 and apparently it's still an
issue with 3.8.

iFolder excludes thumbs.db and .DS_store files by default. While this
is probably a sound decision based on what they are, the iFolder client
pops up a "sync error" balloon in the system tray every time the user
logs in stating that these files are denied by policy.

In trying to resolve this, I've run into a couple of things that look
like bugs in the admin UI:

1. You can't GLOBALLY allow files that have already been denied.

2. Worse yet, once a file type has been added to the global deny list,
it is COPIED to every user and the only way to allow it seems to be to
edit EVERY user and check the file and then hit the allow button. This
is extremely inconvenient from an administrative perspective.

3. There doesn't appear to be a way to "silence" errors for files that
are denied by policy. I can see where there would be situations where
you'd want users to know that certain files aren't being backed up (e.g.
MP3's). However, these thumbs.db files are unimportant and should not
disturb the user with "noise" alerts that teach them to ignore the sync
error balloon. There should be an option to suppress the error globally
based on the individual entry for the disallowed file type.