SMTP 221 Closing Connection vs 535 Authentication Failed
SMTP 221 (Closing Connection) is a 2xx Positive Completion response, while 535 (Authentication Failed) is a 5xx Permanent Negative response. 221 indicates that the server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session. In contrast, 535 means that the authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
Описание
The server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session.
Когда вы это видите
After sending the QUIT command at the end of a mail session. The server acknowledges the disconnect and the TCP connection will be closed.
Как исправить
No fix needed — this is the expected response when ending an SMTP session. If you see this unexpectedly, the server may be shutting down or timing out idle connections.
Описание
The authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
Когда вы это видите
After submitting incorrect credentials via the AUTH command. The username or password does not match any account on the server.
Как исправить
Double-check your username and password. If using an app password (e.g., Gmail, Outlook), ensure it is current and has not been revoked. Also verify the correct SASL mechanism (PLAIN, LOGIN, etc.).
Ключевые различия
221 is a 2xx Positive Completion response, while 535 is a 5xx Permanent Negative response.
SMTP 221: The server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session.
SMTP 535: The authentication credentials provided are invalid. The username, password, or authentication mechanism was rejected by the server.
You encounter 221 when after sending the QUIT command at the end of a mail session. The server acknowledges the disconnect and the TCP connection will be closed.
You encounter 535 when after submitting incorrect credentials via the AUTH command. The username or password does not match any account on the server.
Когда что использовать
For 221 (Closing Connection): No fix needed — this is the expected response when ending an SMTP session. If you see this unexpectedly, the server may be shutting down or timing out idle connections. For 535 (Authentication Failed): Double-check your username and password. If using an app password (e.g., Gmail, Outlook), ensure it is current and has not been revoked. Also verify the correct SASL mechanism (PLAIN, LOGIN, etc.).