///Help message (Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user)
///Help message (Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user)
_214,
///<domain> Service ready
///<domain> Service ready
_220,
///<domain> Service closing transmission channel
///<domain> Service closing transmission channel
_221,
///Authentication successful,
///Authentication successful,
_235,
///Requested mail action okay, completed
///Requested mail action okay, completed
_250,
///User not local; will forward to <forward-path> (See Section 3.4)
///User not local; will forward to <forward-path> (See Section 3.4)
_251,
///Cannot VRFY user, but will accept message and attempt delivery (See Section 3.5.3)
///Cannot VRFY user, but will accept message and attempt delivery (See Section 3.5.3)
_252,
///rfc4954 AUTH continuation request
///rfc4954 AUTH continuation request
_334,
///PRDR specific, eg "content analysis has started|
///PRDR specific, eg "content analysis has started|
_353,
///Start mail input; end with <CRLF>.<CRLF>
///Start mail input; end with <CRLF>.<CRLF>
_354,
///<domain> Service not available, closing transmission channel (This may be a reply to any command if the service knows it must shut down)
///<domain> Service not available, closing transmission channel (This may be a reply to any command if the service knows it must shut down)
_421,
///Requested mail action not taken: mailbox unavailable (e.g., mailbox busy or temporarily blocked for policy reasons)
///Requested mail action not taken: mailbox unavailable (e.g., mailbox busy or temporarily blocked for policy reasons)
_450,
///Requested action aborted: local error in processing
///Requested action aborted: local error in processing
_451,
///Requested action not taken: insufficient system storage
///Requested action not taken: insufficient system storage
_452,
///Server unable to accommodate parameters
///Server unable to accommodate parameters
_455,
///Syntax error, command unrecognized (This may include errors such as command line too long)
///Syntax error, command unrecognized (This may include errors such as command line too long)
_500,
///Syntax error in parameters or arguments
///Syntax error in parameters or arguments
_501,
///Command not implemented (see Section 4.2.4)
///Command not implemented (see Section 4.2.4)
_502,
///Bad sequence of commands
///Bad sequence of commands
_503,
///Command parameter not implemented
///Command parameter not implemented
_504,
///Authentication failed
///Authentication failed
_535,
///Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
///Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
_550,
///User not local; please try <forward-path> (See Section 3.4)
///User not local; please try <forward-path> (See Section 3.4)
_551,
///Requested mail action aborted: exceeded storage allocation
///Requested mail action aborted: exceeded storage allocation
_552,
///Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)
///Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)
_553,
///Transaction failed (Or, in the case of a connection-opening response, "No SMTP service here")
///Transaction failed (Or, in the case of a connection-opening response, "No SMTP service here")
_554,
///MAIL FROM/RCPT TO parameters not recognized or not implemented
///MAIL FROM/RCPT TO parameters not recognized or not implemented