SMTP Cheat Sheet

Basic Commands

Command	Description
telnet <server> 25	Connect to the SMTP server using Telnet
EHLO <domain>	Identify the sending host
MAIL FROM: <address>	Specify the sender’s email address
RCPT TO: <address>	Specify the recipient’s email address
DATA	Start the message data
<message>	Enter the message data
.	End the message data
QUIT	End the session

SMTP Operations

Operation	Description
Connect	Establish a connection to the SMTP server
EHLO	Identify the sending host and request the server’s capabilities
MAIL FROM	Specify the sender’s email address
RCPT TO	Specify the recipient’s email address
DATA	Start the message data
Message	Enter the message data
Quit	End the session

SMTP Response Codes

Code	Description
220	Service ready
221	Service closing transmission channel
250	Requested mail action okay, completed
354	Start mail input; end with <CRLF>.<CRLF>
421	Service not available, closing transmission channel
450	Requested mail action not taken: mailbox unavailable
451	Requested action aborted: local error in processing
452	Requested action not taken: insufficient system storage
500	Syntax error, command unrecognized
501	Syntax error in parameters or arguments
502	Command not implemented
503	Bad sequence of commands
504	Command parameter not implemented
550	Requested action not taken: mailbox unavailable
551	User not local; please try <forward-path>
552	Requested mail action aborted: exceeded storage allocation
553	Requested action not taken: mailbox name not allowed
554	Transaction failed