SMTP Codes de statut
The standard protocol for sending email across the Internet. SMTP reply codes indicate the success or failure of mail transactions.
Voir la spécification →À propos de SMTP
SMTP has been the backbone of email delivery since 1982 (RFC 821), later updated by RFC 5321. An SMTP session follows a structured conversation: the client connects, identifies itself with EHLO, authenticates (if required), specifies sender and recipients via MAIL FROM and RCPT TO commands, then transmits the message body with DATA. At each step, the server replies with a three-digit code. Codes starting with 2xx indicate success, 3xx mean intermediate status (more input expected), 4xx signal temporary failures (try again later), and 5xx indicate permanent errors. Modern email relies on extensions like STARTTLS for encryption, DKIM and SPF for authentication, and DMARC for policy enforcement — all of which produce additional SMTP codes during the handshake.
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200-299 2xx Positive Completion
The requested action has been completed successfully. The mail server has accepted the command and no further action is needed for this step.
A system status reply providing information about the mail server's current state. This is typically sent in response to a …
A help message response containing information about the server's supported commands or a specific command's usage. This is a human-readable …
The SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon …
The server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end …
The client has been successfully authenticated using the AUTH command. The server will now accept mail commands from this authenticated …
The requested mail action has been completed successfully. This is the most common positive response in SMTP, returned after HELO/EHLO, …
The recipient is not local to the server, but it will forward the message to the specified forwarding address. The …
The server cannot verify the user but will accept the message and attempt delivery. This is often returned in response …
300-399 3xx Positive Intermediate
The command has been accepted but the server needs additional information before it can complete the request. The client should send the next expected piece of data.
The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge …
The server is ready to receive the message body. The client should begin sending the email content (headers and body) …
400-499 4xx Transient Negative
The command was not accepted and the requested action did not occur. However, the error is temporary and the client may retry the same command later.
The SMTP service is not available and the server is closing the transmission channel. This may be sent as a …
The requested mail action was not taken because the mailbox is temporarily unavailable. This could be due to the mailbox …
The requested action was aborted due to a local error in processing. The server encountered an internal issue that prevented …
The requested action was not taken because the server has insufficient system storage. The server cannot accept more mail until …
The server is currently unable to accommodate the requested parameters. This is a general temporary failure indicating the server cannot …
500-599 5xx Permanent Negative
The command was not accepted and the requested action will not occur. The error is permanent and the client should not retry the same request without modification.
The server could not recognize the command due to a syntax error. The command line was malformed or the command …
The command was recognized but the parameters or arguments are syntactically invalid. The server understood what you wanted to do …
The command is recognized by the SMTP specification but is not implemented on this server. The server understands the command …
The commands were sent in the wrong order. SMTP requires a specific command sequence (EHLO, MAIL FROM, RCPT TO, DATA) …
A command parameter is not implemented on this server. The command itself is valid but the specific parameter or extension …
The host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all …
The server requires authentication before accepting mail commands. You must issue the AUTH command with valid credentials before attempting to …
The authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
The requested action was not taken because the mailbox does not exist or the recipient address is rejected by policy. …
The recipient is not local to this server and the server does not accept mail for forwarding. Unlike 251, this …
The requested mail action was aborted because the recipient's mailbox has exceeded its storage allocation. Unlike the temporary 452, this …
The requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to …
The mail transaction has failed. This is a catch-all permanent error that can occur at any point during the SMTP …
The destination domain does not accept mail and no forwarding address is available. The domain's DNS configuration (null MX record) …
Guides SMTP
Systematic approach to diagnosing email delivery failures — SMTP transaction tracing, bounce code interpretation, and reputation diagnostics.
SMTP Reply Codes: What Your Email Server Is Telling YouUnderstanding SMTP reply codes — from successful delivery (250) to bounce messages (550) and temporary failures (421).
Improving Email Deliverability: SPF, DKIM, and DMARC SetupA step-by-step guide to setting up email authentication — SPF records, DKIM signing, and DMARC policies to avoid the spam …
Diagnosing Email Bounces: Soft (4xx) vs Hard (5xx)How to read SMTP bounce codes and take the right action — temporary vs permanent failures, common bounce reasons, and …
SMTP Authentication Methods ExplainedA guide to SMTP AUTH mechanisms — PLAIN, LOGIN, CRAM-MD5, OAuth 2.0 — and how STARTTLS and implicit TLS protect …
Email Header Analysis: Tracing Delivery PathHow to read email headers to trace the delivery path, interpret authentication results, and distinguish envelope from header addresses.