地址不详的邮件 meaning in English

blind mail

To improve the mail delivery process , we have developed standard procedures assisting delivery staff to serve customers . in addition , we drew up guidelines on delivering mail that carries an ambiguous address as a further initiative to enhance delivery accuracy
改善邮件派递过程方面，我们亦订明一套标准程序，协助员工服务顾客；又订定派递邮件的指引，载述如何处理地址不详的邮件，务求提升准确派递的水平。