As the number of low-cost Internet-of-Things (IoT) devices increases dramatically in recent years, they have become ideal targets for E-mail spammers. Some network cameras are shipped to the market with default passwords. Operating systems of many IoT devices are often outdated or not well-configured. Those practices make IoT devices easy to be compromised. Some of these compromised IoT devices may be used for E-mail spamming. Hence, how to handle undesired connections from client IoT devices becomes an important issue for mail server administrators. Even though the whitelist or blacklist are adopted by a mail server only allowing to receive E-mails relayed from few trusted SMTP servers, such list-based approach apparently cannot be applied for global SMTP clients when considering to the flexibility and cost of list maintenance. For most mail servers providing SMTP for desktop, laptop, or mobile clients rather than IoT devices, this paper proposes a server-side approach, called IoT detector (IoTD), to detect E-mails which are sent from IoT devices. Because the majority of IoT devices are not used by human users to send E-mail, administrators of mail servers may consider the E-mail sent by an IoT device as spam directly if IoT clients are not expected. Experimental results show that IoTD can accurately detect E-mails sent by IoT devices. The accuracy evaluation among five IoT devices and two non-IoT devices of this study shows that all tests for these five IoT devices are true positives, and all tests for these two non-IoT devices are true negatives as well.

近年来，随着低成本物联网 (IoT) 设备的数量急剧增加，它们已成为垃圾邮件发送者的理想目标。一些网络摄像机在出厂时带有默认密码。许多物联网设备的操作系统通常已经过时或配置不当。这些做法使物联网设备很容易受到攻击。其中一些受感染的物联网设备可能被用于发送垃圾邮件。因此，如何处理来自客户端 IoT 设备的不需要的连接成为邮件服务器管理员的一个重要问题。即使邮件服务器采用白名单或黑名单，只允许接收从少数受信任的 SMTP 服务器转发的电子邮件，但考虑到列表维护的灵活性和成本，这种基于列表的方法显然不适用于全球 SMTP 客户端。IoT 检测器(IoTD)，用于检测从 IoT 设备发送的电子邮件。由于大多数 IoT 设备不是由人类用户使用来发送电子邮件的，因此如果不需要 IoT 客户端，邮件服务器的管理员可能会直接将 IoT 设备发送的电子邮件视为垃圾邮件。实验结果表明，IoTD 可以准确检测 IoT 设备发送的电子邮件。本研究对五台物联网设备和两台非物联网设备的准确度评估表明，这五台物联网设备的测试结果均为真阳性，这两种非物联网设备的测试结果均为真阴性。