SMTP 354 Start Mail Input vs 553 Mailbox Name Invalid
SMTP 354 (Start Mail Input) is a 3xx Positive Intermediate response, while 553 (Mailbox Name Invalid) is a 5xx Permanent Negative response. 354 indicates that the server is ready to receive the message body. The client should begin sending the email content (headers and body) and terminate with a single line containing only a period (CRLF.CRLF). 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.
Descripción
The server is ready to receive the message body. The client should begin sending the email content (headers and body) and terminate with a single line containing only a period (CRLF.CRLF).
Cuándo lo verás
After sending the DATA command. The server is now waiting for you to type or stream the email message, ending with a dot on its own line.
Cómo solucionarlo
Send your message content followed by a line with just a period (.) to signal the end. If you get an error after this, check that your message does not contain a bare period on a line by itself within the body.
Descripción
The requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to the expected format.
Cuándo lo verás
When the sender or recipient address contains invalid characters, improper formatting, or violates the server's naming conventions.
Cómo solucionarlo
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.
Diferencias clave
354 is a 3xx Positive Intermediate response, while 553 is a 5xx Permanent Negative response.
SMTP 354: The server is ready to receive the message body. The client should begin sending the email content (headers and body) and terminate with a single line containing only a period (CRLF.CRLF).
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 354 when after sending the DATA command. The server is now waiting for you to type or stream the email message, ending with a dot on its own line.
You encounter 553 when when the sender or recipient address contains invalid characters, improper formatting, or violates the server's naming conventions.
Cuándo usar cada uno
For 354 (Start Mail Input): Send your message content followed by a line with just a period (.) to signal the end. If you get an error after this, check that your message does not contain a bare period on a line by itself within the body. 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.