SMTP 450 Mailbox Unavailable vs 451 Local Error
Both SMTP 450 (Mailbox Unavailable) and 451 (Local Error) belong to the 4xx Transient Negative category. 450 indicates 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. Meanwhile, 451 means that the requested action was aborted due to a local error in processing. The server encountered an internal issue that prevented it from completing the command.
描述
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.
何时出现
When the recipient's mailbox exists but is currently locked, busy, or subject to greylisting. The server is asking you to try again later.
如何修复
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.
描述
The requested action was aborted due to a local error in processing. The server encountered an internal issue that prevented it from completing the command.
何时出现
When the receiving server hits an internal error such as a database failure, DNS lookup timeout, or anti-spam filter processing error.
如何修复
Retry the message later. If you control the server, check its logs for the specific error — common causes include DNS resolution failures, disk I/O errors, or database connectivity issues.
主要区别
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.
SMTP 451: The requested action was aborted due to a local error in processing. The server encountered an internal issue that prevented it from completing the command.
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.
You encounter 451 when when the receiving server hits an internal error such as a database failure, DNS lookup timeout, or anti-spam filter processing error.
何时使用哪个
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. For 451 (Local Error): Retry the message later. If you control the server, check its logs for the specific error — common causes include DNS resolution failures, disk I/O errors, or database connectivity issues.