Art of email ESMTP SMTP data codes command groups

Command	Code	Description

Connect	220	<domain> Service ready
	421	<domain> Service not available, closing transmission channel

HELO	250	Requested mail action okay, completed
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	504	Command parameter not implemented
	521	<domain> does not accept mail [rfc1846]
	421	<domain> Service not available, closing transmission channel

EHLO	250	Requested mail action okay, completed
	550	Not implemented
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	504	Command parameter not implemented
	421	<domain> Service not available, closing transmission channel

MAIL	250	Requested mail action okay, completed
	552	Requested mail action aborted: exceeded storage allocation
	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
	421	<domain> Service not available, closing transmission channel

RCPT	250	Requested mail action okay, completed
	251	User not local; will forward to <forward-path>
	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
	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
	503	Bad sequence of commands
	521	<domain> does not accept mail [rfc1846]
	421	<domain> Service not available, closing transmission channel


DATA	354	Start mail input; end with <CRLF>.<CRLF>
	451	Requested action aborted: local error in processing
	554	Transaction failed
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	503	Bad sequence of commands
	421	<domain> Service not available, closing transmission channel
ESMTP/SMTP Connect and Data Receive Reply Codes Command Groups Received data
Receive	250	Requested mail action okay, completed
	552	Requested mail action aborted: exceeded storage allocation
	554	Transaction failed
	451	Requested action aborted: local error in processing
	452	Requested action not taken: insufficient system storage

RSET	200	(nonstandard success response, see rfc876)
	250	Requested mail action okay, completed
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	504	Command parameter not implemented
	421	<domain> Service not available, closing transmission channel

SEND	250	Requested mail action okay, completed
	552	Requested mail action aborted: exceeded storage allocation
	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
	421	<domain> Service not available, closing transmission channel

SOML	250	Requested mail action okay, completed
	552	Requested mail action aborted: exceeded storage allocation
	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
	421	<domain> Service not available, closing transmission channel

SAML	250	Requested mail action okay, completed
	552	Requested mail action aborted: exceeded storage allocation
	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
	421	<domain> Service not available, closing transmission channel

VRFY	250	Requested mail action okay, completed
	251	User not local; will forward to <forward-path>
	550	Requested action not taken: mailbox unavailable
	551	User not local; please try <forward-path>
	553	Requested action not taken: mailbox name not allowed
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	502	Command not implemented
	504	Command parameter not implemented
	421	<domain> Service not available, closing transmission channel

EXPN	250	Requested mail action okay, completed
	550	Requested action not taken: mailbox unavailable
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	502	Command not implemented
	504	Command parameter not implemented
	421	<domain> Service not available, closing transmission channel

HELP	211	System status, or system help reply
	214	Help message
	500	Syntax error, command unrecognized
	501	Syntax error in parameters or arguments
	502	Command not implemented
	504	Command parameter not implemented
	421	<domain> Service not available, closing transmission channel

NOOP	200	(nonstandard success response, see http://www.faqs.org/rfcs/rfc876.html
	250	Requested mail action okay, completed
	500	Syntax error, command unrecognized
	421	<domain> Service not available, closing transmission channel

QUIT	221	<domain> Service closing transmission channel
	500	Syntax error, command unrecognized

TURN	250	Requested mail action okay, completed
	502	Command not implemented
	500	Syntax error, command unrecognized
	503	Bad sequence of commands