SMTP, which stands for Simple Mail Transfer Protocol, is a widely used protocol for electronic mail transfer. It is responsible for sending and receiving emails between mail servers. When an email is sent from one server to another, SMTP is used to establish a connection, transfer the message, and then terminate the connection.

TCP (Transmission Control Protocol) is the transport layer protocol utilized by SMTP for electronic mail transfer. TCP is one of the core protocols in the Internet Protocol Suite and is responsible for reliable, ordered, and error-checked delivery of data packets. It provides a connection-oriented communication between two hosts, ensuring that data is delivered in the correct order and without errors.



- Reliability: SMTP requires a reliable transport protocol to ensure that emails are delivered successfully. TCP guarantees reliable delivery by using acknowledgments, timeouts, and retransmissions. If a packet is lost or corrupted during transmission, TCP will retransmit it until it is successfully received.

- Ordering: TCP also ensures that packets are delivered in the same order they were sent. This is crucial for email delivery as the order of the email's content must be preserved.

- Flow Control: TCP implements flow control mechanisms to prevent overwhelming the recipient's network or buffer. This is important for SMTP to prevent congestion and ensure efficient email delivery.

- Connection-oriented: SMTP requires a connection-oriented protocol as it involves a series of requests and responses between the sender and receiver. TCP establishes a connection between the SMTP client and server, allowing for a reliable and orderly exchange of information.

In summary, TCP is the preferred transport layer protocol for SMTP due to its reliability, ordering, flow control, and connection-oriented nature. It ensures that emails are delivered successfully and in the correct order, making it ideal for the reliable transfer of electronic mail.