SMTP 251 User Not Local vs 450 Mailbox Unavailable
SMTP 251 (User Not Local) is a 2xx Positive Completion response, while 450 (Mailbox Unavailable) 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, 450 means that the requested mail action was not taken because the mailbox is temporarily unavailable. This could be due to the mailbox being locked by another process or a temporary policy restriction.
Açıklama
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.
Gördüğünüzde
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.
Nasıl Düzeltilir
No fix needed — the message will be forwarded automatically. To avoid relaying, send directly to the address provided in the server's response.
Açıklama
The requested mail action was not taken because the mailbox is temporarily unavailable. This could be due to the mailbox being locked by another process or a temporary policy restriction.
Gördüğünüzde
When the recipient's mailbox exists but is currently locked, busy, or subject to greylisting. The server is asking you to try again later.
Nasıl Düzeltilir
Retry delivery after a few minutes. If using greylisting, the second attempt will typically succeed. For persistent failures, check if the recipient's mailbox is full or disabled.
Temel Farklar
251 is a 2xx Positive Completion response, while 450 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 450: The requested mail action was not taken because the mailbox is temporarily unavailable. This could be due to the mailbox being locked by another process or a temporary policy restriction.
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 450 when when the recipient's mailbox exists but is currently locked, busy, or subject to greylisting. The server is asking you to try again later.
Hangisini Ne Zaman Kullanmalı
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 450 (Mailbox Unavailable): Retry delivery after a few minutes. If using greylisting, the second attempt will typically succeed. For persistent failures, check if the recipient's mailbox is full or disabled.