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SMTP Responses

  • Last Updated : 11 Aug, 2020

Simple Mail Transfer Protocol (SMTP) responses are sent from server to client. Each response in SMTP begins with three digit code and it may be followed by additional textual information. The leading digits in response indicate category of response. Following are different categories of the responses :

1. Positive completion reply
2. Positive Intermediate reply
3. Transient Negative Completion reply 
4. Permanent Negative Completion reply 

These are explained as follows :

  1. Positive completion reply –
    This reply refers to successfully completion of action. After that new request may be initiated.
  2. Positive Intermediate reply –
    This reply refers to acceptance of command which we are given, but requested action is being held in state of suspension and also pending receipt of further information.
  3. Transient Negative Completion reply –
    This reply refers to that command was not accepted and requested action did not occur. The error condition is temporary in that case and also action may be requested again.



  4. Permanent Negative Completion reply –
    This reply refers that command was not accepted and requested action did not occur.

Various SMTP responses are listed in the following table :

CategoryCodeDescription
Positive
Completion
Reply
211System status and system help reply.
214Help message.
220<domain>service ready.
221<domain>service closing transmission channel.
250Requested mail action okay, completed.
251User not local; the message will be forwarded to <forward-path>.
Positive
Intermediate
Reply
354Start mail input; end with <CRLF>.

Transient

Negative

Completion

Reply

421<domain>service not available, losing transmission channel.
450Requested mail action not taken, mailbox not available ( e.g. Mailbox busy ).
451Requested action aborted; local error in processing.
452Requested action not taken; insufficient system storage system.
Permanent
Negative
Completion
Reply
500Syntax error, command unrecognized.
501Syntax error in parameters or arguments.
502Command not implemented.
503Bad sequence of commands.
504Command parameter not implemented.
550The requested action is not taken due to the unavailability of mailbox ( e.g. Mailbox not found, no access ).
551User not local; please try <forward-path>.
552Requested mail action aborted; exceeded storage allocation.
553The requested action is not taken because the mailbox name does not allowed it (e.g., Mailbox syntax incorrect.).
554Transaction failed.

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