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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
                     9  TCP/IP Electronic Mail Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)

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SMTP Commands
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TCP/IP Electronic Mail Access and Retrieval Protocols and Methods
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SMTP Replies and Reply Codes
(Page 3 of 4)

Common SMTP Reply Codes

Table 255 contains a list of some of the more common SMTP reply codes taken from RFC 2821, in numerical order. For each, I have shown the “typical” reply text specified in the standard, and provided additional descriptive information where I felt it was needed.

Table 255: SMTP Reply Codes

Reply Code

Reply Text



System status or system help reply.



<Help message…>

Used for text sent in reply to the HELP command.


<servername> Service ready.

Greeting message sent when TCP connection is first established to an SMTP server.


<servername> closing transmission channel.

Goodbye message sent in response to a QUIT message.


Requested mail action okay, completed

Indicates successful execution of a variety of commands.


User not local; will forward to <forward-path>

Used when the SMTP receiver agrees to forward a message to a non-local user.


Cannot VRFY user, but will accept message and attempt delivery

Indicates that a server tried to verify an e-mail address, but was not able to do so completely. Usually means the address appears to be valid but it was not possible to positively ascertain this to be true.


Start mail input; end with <CRLF>.<CRLF>

Intermediate reply to a DATA command.


<servername> Service not available, closing transmission channel

Sent in response to any command when the SMTP receiver prematurely terminates the connection. A common reason for this is receipt of a local shutdown command, due for example to a hardware reboot.


Requested mail action not taken: mailbox unavailable

Sent when a mailbox is busy due to another process accessing it.


Requested action aborted: local error in processing

Local processing problem on the server.


Requested action not taken: insufficient system storage.

Time to clean out the server's hard disk! J


Syntax error, command unrecognized

Response to a bad command or one that was too long.


Syntax error in parameters or arguments



Command not implemented

Command is valid for SMTP in general but not supported by this particular server.


Bad sequence of commands

Commands were not sent in the correct order, such as sending the DATA command before the MAIL command.


Command parameter not implemented.



Requested action not taken: mailbox unavailable

Generic response given due to a problem with a specified mailbox. This includes trying to send mail to an invalid address, refusal to relay to a non-local mailbox and so forth.


User not local; please try <forward-path>

Tells the SMTP sender to try a different path; may be used to support mailbox forwarding.


Requested mail action aborted: exceeded storage allocation

User's mailbox is full.


Requested action not taken: mailbox name not allowed

Specification of an invalid mailbox address.


Transaction failed.

General failure of a transaction.

As mentioned before, the actual text string for each reply code is implementation-specific. While the standard specifies “dry” response text such as “Requested action completed” for a 250 message, some servers customize this code, or even give different replies to different 250 messages depending on context. Again, there are examples of this in other topics.

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Version 3.0 - Version Date: September 20, 2005

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