What is the role of an SMTP server in email delivery?

The role of an SMTP server in email delivery centers on its function to forward, accept, and route emails to their intended recipients. SMTP, which stands for Simple Mail Transfer Protocol, is a protocol used specifically for sending and relaying outgoing emails. When a sender composes an email, the SMTP server receives this message and then determines how to appropriately forward it to the destination server. This process involves identifying the recipient's email address, looking up the Mail Exchange (MX) record for the recipient's domain, and sending the email through the internet to the right server, ultimately delivering the email to the recipient’s mailbox.

In contrast, other options do not accurately capture the primary responsibilities of an SMTP server. For instance, retrieving emails from the inbox typically involves protocols such as POP3 or IMAP, which are designed for accessing and managing emails already in an inbox. Encrypting email messages is not a core function of SMTP; while encryption can be applied in email transmission, it is often handled by additional protocols such as TLS. Finally, displaying incoming emails on the client side is the role reserved for email clients, which provide a user interface for reading and managing emails rather than the SMTP server itself.