COMPUTER NETWORKING

Detailed explanation-1: -Originally, the Simple Mail Transfer Protocol (SMTP) used port 25. Today, SMTP should instead use port 587-this is the port for encrypted email transmissions using SMTP Secure (SMTPS). Port 465 is also used sometimes for SMTPS. However, this is an outdated implementation and port 587 should be used if possible.

Detailed explanation-2: -The SMTP transmission channel is a TCP connection established between the sender process port U and the receiver process port L. This connection is used as the transmission channel. This protocol is assigned the port 25, which is L=25 as the default transmission channel for communication between mail servers.

Detailed explanation-3: -Introduction. Many email clients and services use port 25 for SMTP to send out emails. However an ISP (Internet Service Provider) may block port 25 in order to prevent spamming by its customers.