SMTP Status Codes

Server status or help information, in reply to a status or help request.

Specification text: System status reply

Help text meant for a human reader, usually in reply to HELP.

Specification text: Help message

The server is ready. This is usually the greeting right after the connection opens.

Specification text: Service ready

The server is closing the connection, usually in reply to QUIT.

Specification text: Service closing transmission channel

SMTP authentication succeeded.

Specification text: Authentication successful

The requested action completed. After the message content (DATA), it means this server accepted the message; it does not prove final delivery to the mailbox.

Specification text: Requested mail action okay, completed

The recipient is not local to this server, but the server will forward the message to the given path.

Specification text: User not local; will forward to forward-path

The server cannot verify the user (VRFY), but will accept the message and attempt delivery.

Specification text: Cannot verify the user, but will try to deliver

AUTH is in progress: the server sent a base64 challenge and waits for the client's response.

Specification text: Server challenge response (AUTH)

The server is ready for the message content; the client ends it with a line containing only a period.

Specification text: Start mail input; end with CRLF.CRLF

The service is not available and the server is closing the connection. This is temporary; a later retry may succeed.

Specification text: Service not available, closing channel

Check: Retry later. If it persists, look in the server message for a reason, such as a connection or rate limit.

The user must transition to the selected authentication mechanism, typically by authenticating once with PLAIN.

Specification text: A password transition is needed

The action was not taken because the mailbox is temporarily unavailable (for example busy or temporarily blocked by policy).

Specification text: Requested mail action not taken: mailbox unavailable

Check: Retry later. The enhanced code and the server message may say why the mailbox was unavailable.

The server aborted the action because of a local processing error. This is temporary.

Specification text: Requested action aborted: local error in processing

Check: Retry later. If it persists, the receiving server's administrator needs to check its logs.

Not enough system storage. RFC 5321 also uses 452 for too many recipients in one transaction. This is temporary.

Specification text: Requested action not taken: insufficient system storage

Authentication failed because of a temporary server problem, not because the credentials were wrong.

Specification text: Temporary authentication failure

Check: Retry later. This reply alone is no reason to change the password.

The server cannot accommodate the MAIL FROM / RCPT TO parameters right now. This is temporary.

Specification text: Server unable to accommodate parameters

The command was not recognized or has a syntax error. It may also mean the command line was too long.

Specification text: Syntax error, command unrecognized

The command's parameters or arguments have a syntax error, such as a malformed address.

Specification text: Syntax error in parameters or arguments

The server does not implement this command.

Specification text: Command not implemented

Commands were sent in the wrong order, for example RCPT TO before MAIL FROM.

Specification text: Bad sequence of commands

The command is implemented, but the requested parameter is not.

Specification text: Command parameter not implemented

This host does not accept mail at all (RFC 7504). It is sent instead of the 220 greeting.

Specification text: Machine does not accept mail

Check: Check that you connected to the right host, for example the recipient domain's MX records.

Authentication is required before this command.

Specification text: Authentication required

Check: Configure the client to authenticate with SMTP AUTH before sending.

The selected authentication mechanism is weaker than server policy allows for this user.

Specification text: Authentication mechanism is too weak

Check: Use a stronger authentication mechanism that the server supports.

SMTP authentication failed: the credentials were invalid or insufficient.

Specification text: Authentication credentials invalid

Check: Verify the username, password, and server authentication settings.

This authentication mechanism may only be used over an encrypted connection. RFC 4954 lists this code for historical purposes only; current servers should not advertise such a mechanism until the connection is encrypted.

Specification text: Encryption required for requested auth mechanism

Check: Encrypt the connection with TLS (STARTTLS or implicit TLS) before authenticating.

The action was not taken because the mailbox is unavailable, for example not found, no access, or rejected by policy.

Specification text: Requested action not taken: mailbox unavailable

Check: The basic code alone does not say which; read the enhanced code and the server message.

The recipient is not local to this server; the reply may suggest another forward-path to try.

Specification text: User not local; please try forward-path

The action was aborted because a storage allocation was exceeded, such as a message size or mailbox quota.

Specification text: Requested mail action aborted: exceeded storage allocation

The mailbox name is not allowed, for example because its syntax is incorrect.

Specification text: Requested action not taken: mailbox name not allowed

The transaction failed. As the reply to a new connection, it means no SMTP service is available here.

Specification text: Transaction failed

Check: The basic code alone does not say which; read the enhanced code and the server message.

The MAIL FROM / RCPT TO parameters were not recognized or are not implemented.

Specification text: MAIL FROM/RCPT TO parameters not recognized

The recipient's domain does not accept mail (RFC 7504), for example because it publishes a null MX record.

Specification text: Domain does not accept mail

Check: Check that the recipient domain is correct.

No more specific status is given. The class (success, temporary or permanent failure) is the only standardized information.

Specification text: Other undefined Status

Check: Any details are only in the server message, which is not standardized.

Status related to the sender or recipient address, with no more specific detail.

Specification text: Other address status

The destination address is valid.

Specification text: Destination address valid

The mailbox exists, but something about it caused this status; no more specific detail.

Specification text: Other or undefined mailbox status

Status related to the destination mail system, with no more specific detail.

Specification text: Other or undefined mail system status

Status related to the network or routing, with no more specific detail.

Specification text: Other or undefined network or routing status

Status related to the mail delivery protocol, with no more specific detail.

Specification text: Other or undefined protocol status

Status related to the message content or media, with no more specific detail.

Specification text: Other or undefined media error

Status related to security or policy, with no more specific detail.

Specification text: Other or undefined security status

Check: For a failure, the reason is usually only in the server message; the code does not say which policy applied.

No more specific status is given. The class (success, temporary or permanent failure) is the only standardized information.

Specification text: Other undefined Status

Check: Any details are only in the server message, which is not standardized.

Status related to the sender or recipient address, with no more specific detail.

Specification text: Other address status

The destination mailbox address is invalid: the destination does not recognize the mailbox (the part before @).

Specification text: Bad destination mailbox address

Check: Candidates to check: a typo in the address, or the recipient account being removed or renamed.

The sender's address is syntactically invalid.

Specification text: Bad sender's mailbox address syntax

Check: Check the MAIL FROM (envelope sender) address the client sends.

The mailbox exists, but something about it caused this status; no more specific detail.

Specification text: Other or undefined mailbox status

The mailbox exists but is not accepting messages. It may be disabled permanently or only temporarily.

Specification text: Mailbox disabled, not accepting messages

Check: The recipient or their administrator needs to check the account status.

The recipient's mailbox is full: it exceeded a quota or physical capacity.

Specification text: Mailbox full

Check: The recipient needs to free space; a later retry may then succeed.

Status related to the destination mail system, with no more specific detail.

Specification text: Other or undefined mail system status

The destination mail system is out of storage.

Specification text: Mail system full

The destination host is not accepting messages, for example because of an imminent shutdown, excessive load, or maintenance.

Specification text: System not accepting network messages

Status related to the network or routing, with no more specific detail.

Specification text: Other or undefined network or routing status

The destination host did not answer the connection attempt.

Specification text: No answer from host

Check: Check the destination's MX records and whether the destination is reachable from the sending server.

The connection was established but could not complete the transaction, because of a timeout or poor connection quality.

Specification text: Bad connection

A directory server needed to forward the message, such as DNS, was unavailable.

Specification text: Directory server failure

Check: This is usually temporary. Check DNS resolution on the server that reported it.

Status related to the mail delivery protocol, with no more specific detail.

Specification text: Other or undefined protocol status

The message has more recipients than the server accepts in one transaction.

Specification text: Too many recipients

Check: Split the recipients across several transactions.

A command's arguments were invalid or not supported.

Specification text: Invalid command arguments

Status related to security or policy, with no more specific detail.

Specification text: Other or undefined security status

Check: For a failure, the reason is usually only in the server message; the code does not say which policy applied.

The user must transition to the selected authentication mechanism, typically by authenticating once with PLAIN.

Specification text: A password transition is needed

No more specific status is given. The class (success, temporary or permanent failure) is the only standardized information.

Specification text: Other undefined Status

Check: Any details are only in the server message, which is not standardized.

Status related to the sender or recipient address, with no more specific detail.

Specification text: Other address status

The destination mailbox address is invalid: the destination does not recognize the mailbox (the part before @).

Specification text: Bad destination mailbox address

Check: Candidates to check: a typo in the address, or the recipient account being removed or renamed.

The destination system (the part after @) does not exist or cannot accept mail.

Specification text: Bad destination system address

Check: Check the domain part of the address and its DNS (MX) records.

The destination address is syntactically invalid.

Specification text: Bad destination mailbox address syntax

Check: Check the address for invalid characters or formatting.

The sender's address is syntactically invalid.

Specification text: Bad sender's mailbox address syntax

Check: Check the MAIL FROM (envelope sender) address the client sends.

The mailbox exists, but something about it caused this status; no more specific detail.

Specification text: Other or undefined mailbox status

The mailbox exists but is not accepting messages. It may be disabled permanently or only temporarily.

Specification text: Mailbox disabled, not accepting messages

Check: The recipient or their administrator needs to check the account status.

The recipient's mailbox is full: it exceeded a quota or physical capacity.

Specification text: Mailbox full

Check: The recipient needs to free space; a later retry may then succeed.

Status related to the destination mail system, with no more specific detail.

Specification text: Other or undefined mail system status

The destination mail system is out of storage.

Specification text: Mail system full

The destination host is not accepting messages, for example because of an imminent shutdown, excessive load, or maintenance.

Specification text: System not accepting network messages

The destination system does not support features the message requires.

Specification text: System not capable of selected features

Status related to the network or routing, with no more specific detail.

Specification text: Other or undefined network or routing status

The destination host did not answer the connection attempt.

Specification text: No answer from host

Check: Check the destination's MX records and whether the destination is reachable from the sending server.

The connection was established but could not complete the transaction, because of a timeout or poor connection quality.

Specification text: Bad connection

A directory server needed to forward the message, such as DNS, was unavailable.

Specification text: Directory server failure

Check: This is usually temporary. Check DNS resolution on the server that reported it.

The next hop could not be determined because routing information was unavailable, for example DNS returned no usable records for the domain.

Specification text: Unable to route

Check: Check the recipient domain's MX and address (A / AAAA) records.

Status related to the mail delivery protocol, with no more specific detail.

Specification text: Other or undefined protocol status

A protocol command was out of sequence or not supported.

Specification text: Invalid command

A command's arguments were invalid or not supported.

Specification text: Invalid command arguments

During AUTH, the client's base64 response was longer than the server can accept.

Specification text: Authentication Exchange line is too long

Status related to the message content or media, with no more specific detail.

Specification text: Other or undefined media error

The message contains a media type the destination does not support.

Specification text: Media not supported

Status related to security or policy, with no more specific detail.

Specification text: Other or undefined security status

Check: For a failure, the reason is usually only in the server message; the code does not say which policy applied.

The sender is not authorized to send to the destination, for example because of per-host or per-recipient filtering.

Specification text: Delivery not authorized, message refused

Check: The code does not say which policy applied. Check the server message, and when relaying, whether you must authenticate first.

The message requires a security feature, such as secure authentication, that the delivery protocol could not support.

Specification text: Security features not supported

The message could not be validated because it was corrupted or altered.

Specification text: Message integrity failure

Authentication failed: the credentials were invalid or insufficient.

Specification text: Authentication credentials invalid

Check: Verify the username, password, and server authentication settings.

The authentication mechanism is weaker than server policy allows.

Specification text: Authentication mechanism is too weak

This authentication mechanism requires an encrypted connection.

Specification text: Encryption required for requested authentication mechanism

Check: Encrypt the connection with TLS (STARTTLS or implicit TLS) before authenticating.

The message had no DKIM signature that passed verification, and the receiver's policy requires one.

Specification text: No passing DKIM signature found

Check: Check that the sending system signs outgoing mail with DKIM and that the selector's public key is published in DNS.

The message has DKIM signatures that passed verification, but none meets the receiver's local requirements.

Specification text: No acceptable DKIM signature found

The message has DKIM signatures that passed verification, but none has an identifier that matches the author address in the From header.

Specification text: No valid author-matched DKIM signature found

Check: Check whether mail is DKIM-signed with the domain used in the From header.

An SPF check returned "fail", and the receiver's policy rejects that.

Specification text: SPF validation failed

Check: Check that the sending server's IP address is authorized by the SPF record of the sender's domain.

Evaluating SPF resulted in an error, for example a DNS failure or an invalid SPF record.

Specification text: SPF validation error

Check: Check the sender domain's SPF record for syntax errors or too many DNS lookups.

The sending server's IP address failed the receiver's reverse DNS check.

Specification text: Reverse DNS validation failed

Check: Check that the sending IP has a PTR record whose name resolves back to the same IP.

The message failed more than one authentication check. Which mechanisms failed is not specified.

Specification text: Multiple authentication checks failed

Check: Check the sending domain's SPF and DKIM setup; the server message may name the failed checks.