SMTP response codes are numerical codes that are returned to the sender in response to an SMTP request. These codes provide information about the status of the request and can indicate whether the request was successful or if there was an error.
There are many different SMTP response codes, but some of the most common ones include:
- 2xx codes: These codes indicate that the request was successful and that the message was accepted for delivery.
- 4xx codes: These codes indicate that there was an error with the request and that the message was not accepted for delivery. This could be due to a syntax error or a problem with the message itself.
- 5xx codes: These codes indicate that there was an error with the server and that the message was not accepted for delivery. This could be due to a server error or a problem with the recipient's email account.
SMTP response codes are an important tool for troubleshooting issues with email delivery. If you are having problems sending email, you can check the SMTP response codes that you are receiving to help identify the problem and take appropriate action.
Example SMTP response code
"550 5.7.1 Unfortunately, messages from [sender's IP address] weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to..."
In this example, the SMTP error code is "550 5.7.1." This code indicates that the message was not accepted for delivery because the sender's IP address is on the recipient's block list. The error message includes additional information about the cause of the problem and provides a suggestion for how to resolve it.