Can I ask you how you have your DNS-325 Fan set at ? Auto/Off/Low/HI Or Low Hi Setting?
Fan of my NAS is set to "Auto(Off/Low/High)" - this is also confirmed inside log file. I suggest you to check your log file to see what NAS does regarding fan: if NAS stops it, if NAS sets fan Speed to "STOP" or to "LOW", and so on.
Example of my log file:
09:41:39 dlinknas fan_control: Set Fan Speed To "STOP".
09:54:47 dlinknas fan_control: Set Fan Speed To "LOW".
10:15:00 dlinknas fan_control: Set Fan Speed To "STOP".
10:27:07 dlinknas fan_control: Set Fan Speed To "LOW".
10:46:19 dlinknas fan_control: Set Fan Speed To "STOP".
10:57:26 dlinknas fan_control: Set Fan Speed To "LOW".
11:08:33 dlinknas fan_control: Set Fan Speed To "STOP".
18:01:14 dlinknas fan_control: Set Fan-Control Mode To "Auto(Off/Low/High)"
18:14:22 dlinknas fan_control: Set Fan Speed To "LOW".
Unfortunately hdd temp is not included in log file and the SMART test doesn't include the hdd temp, so it is not possible to monitor the hdd temp via email (only using the web management is possible to know hdd temp in real-time).