7.3.1 - Simple Mail Transfer Protocol

Flashcards about Simple Mail Transfer Protocol and related concepts.

Simple Mail Transfer Protocol (SMTP)

A protocol that enables a person to compose a message and send it to another user on their own network or anywhere in the world via the Internet.

Step 1 of Email Transmission

Client submits a new message for delivery to the local S M T P server over secure port 587, and the message is copied to the sent items folder on the local I M P server using secure port 993.

Step 2 of Email Transmission

The local S M T P server uses D N S to lookup the M X record listing an I P address for the remote recipient domain and establishes a session with the remote S M T P server over the unencrypted port 25.

Step 3 of Email Transmission

If the remote server accepts the message, it copies it to the inbox folder of the user’s mailbox hosted on an I M P server.

Step 4 of Email Transmission

The remote user’s mail client connects to its I M A P server over secure port 993 to download the message.

STARTTLS

A command that upgrades an existing insecure connection to use TLS; also referred to as explicit TLS or opportunistic TLS; now deprecated but remains in widespread use.

Implicit TLS

Establishes the secure connection before any SMTP commands are exchanged; now considered the preferred method.

Port 25

Used for message relay between SMTP servers, or message transfer agents (MTAs); STARTTLS can be used for a secure connection if supported by both servers.

Port 465

Used for SMTP Submission with implicit TLS; SMTP Submission allows the MSA (part of a mail client) to transfer messages for delivery by a server.

Port 587

Used for SMTP Submission with explicit TLS; servers should use STARTTLS and require authentication before message submission.

Simple Mail Transfer Protocol (SMTP)

Specifies how email is delivered from one system to another.

Domain Name System (DNS)

The SMTP servers for the domain are registered in DNS using mail exchange (MX) and host (A/AAAA) records.

Non-Delivery Report (NDR)

If there is a communication problem, the SMTP server retries at regular intervals before timing out and returning an error code indicating the reason the item could not be delivered.

Transport Layer Security (TLS)

SMTP communications can be secured using TLS with a certificate on the SMTP server and a negotiation between client and server about which cipher suites to use.