What do the error codes mean when I try to send emails?

Sometimes email programs, like Outlook, return error messages when trying to send an email. Below are the most common error codes.

1. SMTP 421 Service not available, closing transmission channel. This response is sent by the SMTP Server to a remote SMTP Server or SMTP Client to indicate that the SMTP Server is not available at that moment.

2. SMTP 450 Requested mail action not taken: mailbox unavailable. This response is sent by the server to indicate that a message could not be delivered to the local recipient because your mailbox is full, possibly receiving another email at that moment.

3. SMTP 451 Requested action aborted: local error in processing. This response is obtained when the SMTP Server encounters an error while processing an SMTP transaction.

4. SMTP 452 Requested action not taken: insufficient system storage. There is not enough space in the account to store the message.

5. SMTP 500 Syntax error, command unrecognized. Indicates that the server could not interpret a command that was sent to the SMTP Server or remote SMTP Client.

6. SMTP 501 Syntax error in parameters or arguments. Indicates that the server identified an attempt to send an SMTP command but the parameters associated with it contained a syntax error.

7. SMTP 502 Command not implemented. Indicates that a requested feature or command to the server could not be delivered because it is disabled or not implemented in the MailEnable SMTP connector.

8. SMTP 504 Command parameter not implemented. Indicates that the command sent to the MailEnable SMTP connector contained another command that could not be processed in the same transaction.

9. SMTP 550 Requested action not taken: mailbox unavailable or is not local. Indicates that the recipient's address is not hosted on that server and that relay options prevent the message from being forwarded to the correct recipient.

10. SMTP 551 User not local; please try again. Indicates that the recipient specified in the RCPT command is not locally hosted on the server and that relay options prevent the message from being forwarded to the recipient.

11. SMTP 552 Requested mail action aborted: exceeded storage allocation. This response is obtained from the server when a RCPT or DATA command is given and the user has exceeded their email storage capacity.

12. SMTP 553 Requested action not taken: mailbox name not allowed. Indicates that the format of an SMTP address specified in the RCPT command is incorrect or not properly formatted.

13. SMTP 554 Transaction failed. This is a generic server response when an SMTP transaction fails. This typically occurs when too many processing errors are received.

14. SMTP 214 Help message. Information on how to use the receiver or the meaning of some non-standard command; it is a useful response only for the human user.