SMTP 251 User Not Local vs 452 Insufficient Storage
SMTP 251 (User Not Local) is a 2xx Positive Completion response, while 452 (Insufficient Storage) is a 4xx Transient Negative response. 251 indicates that the recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient. In contrast, 452 means that the requested action was not taken because the server has insufficient system storage. The server cannot accept more mail until storage is freed.
Descripción
The recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient.
Cuándo lo verás
When sending to a recipient whose mailbox is hosted on a different server. The current server knows the forwarding address and will relay the message on your behalf.
Cómo solucionarlo
No fix needed — the message will be forwarded automatically. To avoid relaying, send directly to the address provided in the server's response.
Descripción
The requested action was not taken because the server has insufficient system storage. The server cannot accept more mail until storage is freed.
Cuándo lo verás
When the mail server's disk is full or the recipient's mailbox has exceeded its storage quota. The server cannot store additional messages.
Cómo solucionarlo
If you are the sender, retry later after the recipient frees up space. If you manage the server, clear disk space, increase quotas, or archive old messages.
Diferencias clave
251 is a 2xx Positive Completion response, while 452 is a 4xx Transient Negative response.
SMTP 251: The recipient is not local to the server, but it will forward the message to the specified forwarding address. The server acts as a relay for this recipient.
SMTP 452: The requested action was not taken because the server has insufficient system storage. The server cannot accept more mail until storage is freed.
You encounter 251 when when sending to a recipient whose mailbox is hosted on a different server. The current server knows the forwarding address and will relay the message on your behalf.
You encounter 452 when when the mail server's disk is full or the recipient's mailbox has exceeded its storage quota. The server cannot store additional messages.
Cuándo usar cada uno
For 251 (User Not Local): No fix needed — the message will be forwarded automatically. To avoid relaying, send directly to the address provided in the server's response. For 452 (Insufficient Storage): If you are the sender, retry later after the recipient frees up space. If you manage the server, clear disk space, increase quotas, or archive old messages.