1939年底,国民党军队在广西南宁附近集结兵力,准备反击盘踞昆仑关的日军第5师团等部。为了防范日本特务刺探情报,军统加强了包括邮件检查、电话监听等一系列的保密措施。一个偶然的机会,军统南宁站特工在临近前线的苏圩邮局发现一个奇怪现象,有个中年男人几乎每天都要向沦陷区广州投寄信件,而且每封信上面贴的邮票都有所不同,但通过秘密搜查,并没有在信中找到机密内 At the end of 1939, Kuomintang troops gathered their forces in Nanning, Guangxi, preparing to fight the 5th Division and other units of the Japanese army, which occupied the Kunlun Pass. In order to prevent the Japanese spies spying on intelligence, the military unification strengthened a series of security measures including e-mail inspection and telephone interception. By chance, the agent Nanning Railway Station found a strange phenomenon at the post office near the front of Su Wei. A middle-aged man posed letters to the enemy-occupied area of ​​Guangzhou almost daily, and the stamps attached to each letter were different , But through secret searches did not find the confidentiality within the letter