Special Dot Files

Name	Description
`.SyncID`	A file containing the unique, internal `ID` of the folder. This file should not be manually modified, or deleted. If you do, the folder will no longer be recognised in BitTorrent Sync.
`.SyncIgnore`	A user editable file allowing you to "exclude" certain files/sub folders for being sync'd
`.SyncArchive`	BitTorrent Sync, by default, won't actually delete any of your files/folders. If a corresponding file/folder is deleted on another device, it will simply be "moved" into the .SyncArchive folder on all other devices, rather than being permanently deleted. (In Sync pre v1.1.40, this folder was named .SyncTrash and was later renamed to .SyncArchive as this folder now stores both local files deleted on remote devices, as well as "versioned" files)
`.!Sync files`	Temporary files created by BitTorrent Sync when receiving incoming data transfers. Once a file is fully received, it is then renamed to have its .!Sync extension removed, for example `file.mp3`will become`file.mp3.!Sync` on receiving devices until all data for the file is fully received, at which point it will be renamed back to "file.mp3".
`.SyncPart` and`.SyncTemp`	These are part of the syncing process. Data deltas are downloaded to a `.SyncPart` file. When the download is completed, the original file is checked if it has changed in the middle of the transfer. If the file has not changed, it is copied to `.SyncArchive` as a previous version of the file if the file size is less than `max_file-size_for_versioning`. The file is then renamed to `.SyncTemp` and the patch is applied. Finally, the file is renamed from `.SyncTemp` to the destination filename.
`.SyncOld`	Usually contains a backup of a file when that file gets transferred to your device partially from another location. After the transfer is successful, the `.syncold` file gets moved to `.SyncArchive` folder (if allowed in settings).

Unsafe Directories and Files

Some files should be excluded when syncing user-profiles. This includes local data that is frequently bound to the machine being used.

Name	Comments
`.*`	All Unix-like dot files that store temporary settings.
`ehthumbs.db`	Thumbnails created by software.
`desktop.ini`	Folder settings used by Windows.
`Thumbs.db`	Thumbnail databases (for preview icons and such).
`Library`	Used on OSX to store settings local to the current user.
`Desktop`	Desktops should not be synced.
`Public`	Public folders for sharing.
`Downloads`	Used on Windows and OSX as a common temporary storage of downloaded files.
`Applications`	Used for applications installed locally to the current user.
`Maildir`	The `maildir` e-mail format inbox.
`Music/iTunes`	`iTunes` does not work well with syncing.
`mail`	The `mbox` e-mail format inbox.