简单邮件传输协议(SMTP)响应从服务器发送到客户端。 SMTP中的每个响应均以三位数代码开头,并且其后可能还有其他文本信息。响应中的前两位数字表示响应的类别。以下是响应的不同类别:
1. Positive completion reply
2. Positive Intermediate reply
3. Transient Negative Completion reply
4. Permanent Negative Completion reply
这些解释如下:
- 积极完成答复–
此答复是指成功完成操作。之后,可以发起新请求。 - 积极的中级答复–
此答复指的是接受我们的命令,但请求的操作处于暂停状态,并且有待进一步接收信息。 - 瞬态负完成答复–
此答复表示该命令未被接受,并且未发生请求的操作。在这种情况下,错误状态是暂时的,可能还会再次请求采取措施。 - 永久否定完成回复–
此答复表示该命令未被接受,并且未发生请求的操作。
下表列出了各种SMTP响应:
Category | Code | Description |
---|---|---|
Positive Completion Reply |
211 | System status and system help reply. |
214 | Help message. | |
220 | ||
221 | ||
250 | Requested mail action okay, completed. | |
251 | User not local; the message will be forwarded to |
|
Positive Intermediate Reply |
354 | Start mail input; end with |
Transient Negative Completion Reply |
421 | |
450 | Requested mail action not taken, mailbox not available ( e.g. Mailbox busy ). | |
451 | Requested action aborted; local error in processing. | |
452 | Requested action not taken; insufficient system storage system. | |
Permanent Negative Completion Reply |
500 | Syntax error, command unrecognized. |
501 | Syntax error in parameters or arguments. | |
502 | Command not implemented. | |
503 | Bad sequence of commands. | |
504 | Command parameter not implemented. | |
550 | The requested action is not taken due to the unavailability of mailbox ( e.g. Mailbox not found, no access ). | |
551 | User not local; please try |
|
552 | Requested mail action aborted; exceeded storage allocation. | |
553 | The requested action is not taken because the mailbox name does not allowed it (e.g., Mailbox syntax incorrect.). | |
554 | Transaction failed. |