SMTP 334 Server Challenge vs 521 Host Does Not Accept Mail
SMTP 334 (Server Challenge) is a 3xx Positive Intermediate response, while 521 (Host Does Not Accept Mail) is a 5xx Permanent Negative response. 334 indicates that the server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to. In contrast, 521 means that the host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
คำอธิบาย
The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to.
เมื่อคุณพบเห็น
During the AUTH command handshake. The server is prompting you for your username or password (Base64-encoded) as part of the multi-step authentication process.
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Respond with the appropriate Base64-encoded credentials. If authentication keeps failing after responding, verify your credentials and ensure you are using the correct SASL mechanism.
คำอธิบาย
The host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
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When connecting to a server that has been intentionally configured to refuse all email, such as a domain that only sends but never receives mail.
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Verify you are connecting to the correct mail server by checking the domain's MX records. If the domain truly does not accept mail, contact the recipient through an alternative channel.
ความแตกต่างหลัก
334 is a 3xx Positive Intermediate response, while 521 is a 5xx Permanent Negative response.
SMTP 334: The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to.
SMTP 521: The host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
You encounter 334 when during the AUTH command handshake. The server is prompting you for your username or password (Base64-encoded) as part of the multi-step authentication process.
You encounter 521 when when connecting to a server that has been intentionally configured to refuse all email, such as a domain that only sends but never receives mail.
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For 334 (Server Challenge): Respond with the appropriate Base64-encoded credentials. If authentication keeps failing after responding, verify your credentials and ensure you are using the correct SASL mechanism. For 521 (Host Does Not Accept Mail): Verify you are connecting to the correct mail server by checking the domain's MX records. If the domain truly does not accept mail, contact the recipient through an alternative channel.