The directory to log cached files when using AS2 restart functionality.
If this property is set, the class will cache all data to the RestartDirectory. Thus, when sending a file is interrupted, the class can restart the transmission of the file starting where it was interrupted.
To use this functionality, simply set the RestartDirectory and call Restart.
When using restart functionality, the data is completely processed to the RestartDirectory before sending begins.
NOTE: This directory will not automatically be cleaned up.