SMTP and POP - a short summary

Short Description of SMTP, POP2 and POP3

Simple Mail Transfer Protocol (SMTP):

Is the TCP/IP mail delivery protocol. It moves mail across the Internet and across your local network. It runs over the reliable, connection-oriented service provided by Transmission Control Protocol (TCP), and it uses well known port number 25.

SMTP (port 25)

Command Syntax Function
Hello HELLO <sending-host> Identify sending SMTP

From MAIL FROM:<from-addresses> Sender address

Recipient RCPT TO:<to-address> Recipient address

Data DATA Begin a message

Reset RSET Abort a message

Verify VRFY <string> Verify a username

Expand EXPN <string> Expand a mailing list

Help HELP <string> Request on-line help

Quit QUIT End the SMPT session

SMPT is such a simple protocol you can literally do it yourself. You telnet to port 25 (telnet mail.microsoft.com 25) on a remote host and type mail in from the command line using the SMTP commands.

SMTP provides direct end-to-end mail delivery. This is unusual, most mail systems use store and forward protocols that move mail toward its destination one hop at a time, storing the complete message at each hop and then forwarding it on the next system until final delivery is made. If the direct end-to-end mail delivery fails, the local system knows it right away.

Post Office Protocol (POP):

Is used to transfer the contents of the user's mailbox from the server to the users desktop. POP2 uses port 109 and POP3 uses port 110. These are incompatible protocols that use different commands, but they perform the same basic functions. The POP protocols verify the PC user's login name and password, and move the user's mail from the server to the PC where it is read using a local PC mail reader.

POP2 (port 109)

Command Syntax Function

Hello HELLO user password Identify user account

Folder FOLD mail-folder Select mail folder

Read READ [n] Read mail, start with message n

Retrieve RETR Retrieve message

Save ACKS Acknowledge and save

Delete ACKD Acknowledge and delete

Failed NACK Negative acknowledge

Quit QUIT End the POP2 session

POP3 (port 110)

Syntax Function

USER username The user's account name

PASS password The user's password

STAT Display the number of unread messages/bytes

RETR n Retrieve message number n

DELE n Delete message number n

LAST Display the number of the last message accessed

LIST [n] Display the size of message n or of all messages

RSET Undelete all message, reset message number to 1

TOP n l Print the header and l lines of message n

NOOP Do nothing

QUIT End the POP3 session

Command	Syntax	Function
Hello	HELLO <sending-host>	Identify sending SMTP
From	MAIL FROM:<from-addresses>	Sender address
Recipient	RCPT TO:<to-address>	Recipient address
Data	DATA	Begin a message
Reset	RSET	Abort a message
Verify	VRFY <string>	Verify a username
Expand	EXPN <string>	Expand a mailing list
Help	HELP <string>	Request on-line help
Quit	QUIT	End the SMPT session

Syntax	Function
USER username	The user's account name
PASS password	The user's password
STAT	Display the number of unread messages/bytes
RETR n	Retrieve message number n
DELE n	Delete message number n
LAST	Display the number of the last message accessed
LIST [n]	Display the size of message n or of all messages
RSET	Undelete all message, reset message number to 1
TOP n l	Print the header and l lines of message n
NOOP	Do nothing
QUIT	End the POP3 session