What protocol is used when sending a Word document as an attachment in an email?

When sending a Word document as an attachment in an email, the Simple Mail Transfer Protocol (SMTP) is typically used. SMTP is the standard protocol for sending emails across the Internet. It facilitates the transfer of messages, including email content and any attachments, from the sender's email client to the recipient's email server.

SMTP operates primarily in a push model, where the email client pushes the message to the email server. It supports various types of attachments, allowing files like Word documents to be included as part of the communication. This capability is essential for sending files, documents, and other data necessary for effective email communication.

While other protocols mentioned serve different purposes, they do not specifically handle the process of sending email messages with attachments. For example, SNMP (Simple Network Management Protocol) is used for network management and monitoring, SFTP (Secure File Transfer Protocol) is intended for secure file transfer, and SCTP (Stream Control Transmission Protocol) is utilized for reliable message transmission in telecommunications. These protocols do not fulfill the role of sending email, making SMTP the correct choice for this scenario.