Respuestas SMTP - ERROR 4XX Y 5XX
Las respuestas SMTP proporcionan una breve explicación de por qué no se entregó un mensaje de correo electrónico.
Los códigos de respuesta, los subcódigos y los mensajes varían entre los proveedores de correo, pero deben cumplir con las especificaciones de RFC relevantes.
Los códigos de respuesta para la entrega fallida se dividen en dos categorías: Diferido (4xx) y Rechazado (5xx).
Los códigos de aplazamiento y rechazo indican problemas temporales y permanentes, respectivamente, que impiden la entrega a uno o más destinatarios.
APLAZAMIENTOS (CÓDIGOS 4XX)
Un error 4xx indica una falla temporal, lo que significa que la entrega no se puede completar en este momento. En caso de aplazamiento, el remitente debe volver a intentar la entrega más tarde. Un ejemplo de una falla temporal sería un buzón que recibe demasiado correo en un corto período de tiempo, lo que hace que se difiera parte del correo para una entrega posterior.
RECHAZOS (CÓDIGOS 5XX)
Un error 5xx indica una falla permanente. Este error significa que hay un problema con el contenido, el formato o los destinatarios del mensaje que impide la entrega. Estos problemas deben resolverse antes de que se pueda volver a intentar la entrega reenviando el mensaje. En la mayoría de los casos, el mensaje contenido en la respuesta SMTP indicará el problema específico con el mensaje.
Un ejemplo de falla permanente es un mensaje enviado a un destinatario que no existe. Códigos de aplazamiento CONNECT Código SMTP Subcódigo SMTP Código de soporte Mensaje de rebote
CONNECT
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 421 | G2 |
"Too many concurrent connections from this client (G2)" |
|
| 450 | 4.7.1 | G1F |
"4.7.1 Client host {IP} has no PTR record (G1F)" |
RCPTTO
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 450 | 4.4.1 | G6 | "4.4.1 {EMAIL}: The recipient's server was temporarily unavailable to accept your message (G6)" A temporary failure while attempting to verify the recipient address |
| 450 | 4.2.1 | G30 | "Mailbox received too much email in a short period of time" We rate limit inbound email to mailboxes to protect the entire system |
| 451 | 4.7.1 | G28 | "Received too many messages from a new or untrusted IP" We require that incoming IPs establish good sending behavior before sending large volumes of mail to our platform |
DATA
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 450 | 4.4.6 | G16 | "4.4.6 Routing loop detected (G16)" An undeliverable mail loop was detected |
| 450 | 4.4.0 | G1E |
"4.4.0 {EMAIL}: Temporary DMARC DNS lookup failure (G1E)"A temporary failure while looking up sender's DMARC policy |
Rejection Codes
CONNECT
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 550 | 5.7.0 | G1A | "5.7.0 mime_banned_file - Your message has been rejected because it contains a banned file attachment (G1A)" Block messages with .exe files in attached archives |
MAILFROM
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 550 | 5.0.0 | G29 | "Received too many messages from a sender mailbox" We rate limit the email of senders to our platform to protect our system |
RCPTTO
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 550 | 5.1.1 | G8, G9 | "5.1.1 {EMAIL}: Email address could not be found, or was misspelled (G8, G9)" Recipient address does not exist on our system |
| 550 | 5.7.1 | G7 | "5.7.1 {EMAIL}: The recipient's server refused to accept your message (G7)" A permanent failure while attempting to verify the recipient address |
| 554 | 5.7.1 | GE | "5.7.1 {EMAIL}: Sender address rejected: Blocked by this recipient" |
| 550 | 5.7.1 | G14 | "5.7.1 {EMAIL}: Sender's MX record not allowed (G14)" The senders domain's MX records match a blocklisted provider |
| 554 | 5.7.1 | G31 | "5.7.1 ACL dns\_rbl; Client host [${ip}] blocked using ${zone}=${result} Senderscore. Please visit https://senderscore.org/rtbl/ for more information on why this message could not be delivered (G31)" Sender's ip is blocked by Senderscore |
| 554 | 5.7.1 | G32 | "5.7.1 ACL dns\_rbl; Client host [${ip}] blocked using ${zone}=${result} Spamhaus XBL. Please visit http://www.spamhaus.org/lookup/ for more information on why this message could not be delivered (G32)" Sender's ip is blocked by Spamhaus XBL |
DATA
| SMTP code | SMTP subcode | Support Code | Bounce Message / Meaning |
|---|---|---|---|
| 550 | 5.1.0 | R2 | "Sender is not allowed to send from {MAIL FROM DOMAIN}" |
| 550 | 5.1.1 | G8, G9 | "5.1.1 {EMAIL}: Email address could not be found, or was misspelled (G8, G9)" Recipient address does not exist on our system |
| 550 | 5.7.1 | G3, G4, G5 | "5.7.1 Virus found (G3,G4,G5)" Message was identified as a virus by our content filter |
| 550 | 5.7.1 | G15 | "5.7.1 Email rejected per DMARC policy for {DMARC DOMAIN} (G15)" Message failed DMARC validation |
| 550 | 5.7.0 | G18 | "5.7.0 header_contenttype_1 (G18)" Rejected for matching a known virus signature |
| 550 | 5.7.0 | G19 | "5.7.0 header_contenttype_2 - Multi-part MIME messages are rejected as dangerous (G19)" Partial MIME messages are not supported |
| 550 | 5.7.0 | G1A | "5.7.0 mime_banned_file - Your message has been rejected because it contains a banned file attachment (G1A)" Executables in compressed attachments are not allowed |
| 550 | 5.7.0 | G1B | "5.7.0 mime_banned_file - Your message has been rejected because it contains a banned file attachment (G1B)" File Types that exploit vulnerabilities in Windows programs are not allowed |
| 550 | 5.7.0 | G1C | "5.7.0 mime_banned_file - File attachment is not allowed because they can be used to exploit Winzip (G1C)" Messages with attachment file extensions linked to WinZip vulnerabilities are not allowed |
| 550 | 5.7.0 | G1D | "5.7.0 mime_banned_file - CLSID file extensions are dangerous (G1D)" Messages with attachment file names containing Windows classIDs are not allowed |
Ref. rackspace.com