SMTP 220 Service Ready vs 553 Mailbox Name Invalid
SMTP 220 (Service Ready) is a 2xx Positive Completion response, while 553 (Mailbox Name Invalid) is a 5xx Permanent Negative response. 220 indicates that the SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identificati In contrast, 553 means that the requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to the expected format.
説明
The SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identification.
このコードが表示される場合
Immediately after establishing a TCP connection to the mail server on port 25, 465, or 587. This is the server's welcome banner confirming it is ready to accept commands.
解決方法
No fix needed — this confirms a successful connection. If you do not receive this greeting, check that the server is running, the port is correct, and no firewall is blocking the connection.
説明
The requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to the expected format.
このコードが表示される場合
When the sender or recipient address contains invalid characters, improper formatting, or violates the server's naming conventions.
解決方法
Check the email address format — ensure it follows the standard [email protected] pattern with valid characters. Remove any spaces, special characters, or encoding issues from the address.
主な違い
220 is a 2xx Positive Completion response, while 553 is a 5xx Permanent Negative response.
SMTP 220: The SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identificati
SMTP 553: The requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to the expected format.
You encounter 220 when immediately after establishing a TCP connection to the mail server on port 25, 465, or 587. This is the server's welcome banner confirming it is ready to accept commands.
You encounter 553 when when the sender or recipient address contains invalid characters, improper formatting, or violates the server's naming conventions.
どちらをいつ使うか
For 220 (Service Ready): No fix needed — this confirms a successful connection. If you do not receive this greeting, check that the server is running, the port is correct, and no firewall is blocking the connection. For 553 (Mailbox Name Invalid): Check the email address format — ensure it follows the standard [email protected] pattern with valid characters. Remove any spaces, special characters, or encoding issues from the address.