Builder · Lesson 15

How do mail and file-transfer protocols differ?

SMTP sends mail, POP3 retrieves it, IMAP synchronizes a remote mailbox, while FTP, FTPS, and SFTP move files with different security models.

Three mail jobs

Sending, retrieving, and synchronizing are different operations.

SMTP submits and relays messages between mail systems. POP3 retrieves messages, traditionally by downloading them to a client. IMAP keeps the mailbox on the server and synchronizes folders, flags, and message state across clients.

FTP-family protocols expose file operations such as listing, reading, writing, and transferring files. Their security properties depend on which protocol is used and how it is configured.

SMTP is not a mailbox-reading protocol.SMTP moves a message toward its destination; POP3 and IMAP let a user agent access the delivered mailbox. FTPS adds TLS to FTP, while SFTP is a file-transfer subsystem carried over SSH.

Build the model

Six protocol choices

01

SMTP

Submits and relays mail, commonly using TCP 25, 465, or 587 depending on the role and TLS mode.

02

POP3

Retrieves messages from a mailbox, commonly through TCP 110 or protected POP3S on TCP 995. It is oriented toward client-side retrieval.

03

IMAP

Maintains a server-side mailbox view, with folders, flags, search, and synchronization; commonly TCP 143 or protected IMAPS on TCP 993.

04

FTP

Transfers files with a control connection and a separate data connection; classic FTP does not encrypt credentials or content.

05

FTPS

Uses FTP semantics with TLS protection, while retaining FTP’s control and data channel model.

06

SFTP

Uses an SSH connection for file operations; it is not FTP with an “S” added.

Follow the paths

One mailbox, three mail operations

SMTP moves messages between systems. POP3 downloads messages to a client, while IMAP keeps the client and the server-side mailbox synchronized. The file-transfer paths remain separate application jobs.

SMTP sends mail from a client through a mail system to remote mail, while POP3 downloads messages and IMAP synchronizes the mailbox.
SMTP sends and relays; POP3 retrieves; IMAP synchronizes the mailbox.

Knowledge check

Test your application protocol model

Answer six questions.

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