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Online SMTP Response

SMTP = Simple Mail Transfer Protocol.SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred. It is a client-server protocol, where the client transmits an email message to the server. Either an end-user's email client, a.k.a. MUA (Mail User Agent), or a relaying server's MTA (Mail Transfer Agents) can act as an SMTP client.
Source: WikiPedia

 

Example: smtp.gmail.com


If you select Advanced Output, the complete header response will be shown.
If not, only the first SMTP response is shown.


SMTP response codes:

211    System status, or system help reply.
214    Help message.
220    Domain service ready.
         Ready to start TLS.
221    Domain service closing transmission channel.
250    OK, queuing for node node started.
         Requested mail action okay, completed.
251    OK, no messages waiting for node node.
         User not local, will forward to forwardpath.
252    OK, pending messages for node node started.
         Cannot VRFY user (e.g., info is not local), but will take message for this user and attempt delivery.
253    OK, messages pending messages for node node started.
354    Start mail input; end with <CRLF>.<CRLF>.
355    Octet-offset is the transaction offset.
421    Domain service not available, closing transmission channel.
432    A password transition is needed.
450    Requested mail action not taken: mailbox unavailable.
         ATRN request refused.
451    Requested action aborted: local error in processing.
         Unable to process ATRN request now
452    Requested action not taken: insufficient system storage.
453    You have no mail.
454    TLS not available due to temporary reason.
         Encryption required for requested authentication mechanism.
458    Unable to queue messages for node node.
459    Node node not allowed: reason.
500    Command not recognized: command.
         Syntax error.
501    Syntax error, no parameters allowed.
502    Command not implemented.
503    Bad sequence of commands.
504    Command parameter not implemented.
521    Machine does not accept mail.
530    Must issue a STARTTLS command first.
         Encryption required for requested authentication mechanism.
534    Authentication mechanism is too weak.
538    Encryption required for requested authentication mechanism.
550    Requested action not taken: mailbox unavailable.
551    User not local; please try forwardpath.
552    Requested mail action aborted: exceeded storage allocation.
553    Requested action not taken: mailbox name not allowed.
554    Transaction failed.