Which protocol provides a simple email transfer service by moving messages between mail servers on the Internet (store-and-forward) and defines how senders hand off mail to a server?

Introduction:
Email relies on multiple protocols with distinct roles. Understanding which one actually transfers mail between servers (and accepts mail from clients for relay) is crucial for configuring MX records, troubleshooting delivery, and securing mail flows.

Given Data / Assumptions:

• We need the protocol responsible for server-to-server message transport.
• “Simple email service” here refers to the base transfer protocol, not mailbox access.
• We compare SMTP with IMAP/POP3 (mailbox access) and unrelated protocols.

Concept / Approach:
Simple Mail Transfer Protocol (SMTP) handles mail submission (from clients to servers) and relay (between servers). It is a text-based protocol that uses a store-and-forward model and commonly operates on TCP ports 25 (relay), 587 (submission), and 465 (implicit TLS). In contrast, POP3 and IMAP are mailbox access protocols used by clients to retrieve or manage messages; they do not move mail between servers. DHCP leases IP addresses; FTP transfers generic files but is not the email transport protocol.

Step-by-Step Solution:
1) Identify required function: server-to-server mail transfer.2) Map function to SMTP.3) Differentiate from POP3/IMAP which are for mailbox access.4) Select SMTP as the correct answer.

Verification / Alternative check:
Mail logs and headers show “Received:” lines added by each SMTP hop, demonstrating SMTP’s role in relaying messages across the Internet.

Why Other Options Are Wrong:

• IMAP: mailbox synchronization/management.
• DHCP: address configuration, unrelated to email.
• FTP: file transfer, not email.
• POP3: mailbox retrieval, not inter-server relay.

Common Pitfalls:
Assuming POP3 “moves” email; it retrieves from a mailbox but does not relay between servers.

Final Answer:
SMTP