- What is SMTP?
- What are the “Response Codes”?
- Common bounce errors and troubleshooting
- Okta Classic Engine
- Okta Identity Engine (OIE)
- SMTP (Simple Mail Transfer Protocol)
- Response Codes
What is SMTP?
SMTP (Simple Mail Transfer Protocol) is a TCP/IP type of protocol used in sending and receiving email. SMTP is used most commonly by email clients, including Gmail, Outlook, Apple Mail and Yahoo Mail.
An SMTP server is an application or computer that sends, receives and relays email.
What are the “Response Codes”?
Each SMTP call returns a response. 200 responses are usually success responses, and 400 responses are usually deferrals. SendGrid continues to retry resending 400 messages for up to 72 hours. 500 responses are hard failures that are not retried by our servers. The list below has possible response codes with example errors and a general explanation.
Common SendGrid error messages and troubleshooting:
| Error Code 550 | |
| Requested action not taken: Mailbox unavailable | You are temporarily blocked from sending emails due to repeated bad requests. |
| This error is caused when the user’s mailbox was unavailable. Usually, this is because it could not be found or because of incoming policy reasons. Remove the address(es) from the list - it may be fake, or it was mistyped. | Too many bad requests, such as bad sender or bad recipient address, have been sent in a short time frame. A temporary block of a few minutes has been activated to prevent more bad requests until a fix can be implemented. |
| Error Code 551 |
| User does not exist. |
| The intended mailbox does not exist on the recipient server. Remove the address(es) from the list. |
| Error Code 552 |
|
This message is larger than the current system limit or the recipient’s mailbox is full. |
| The recipient's mailbox has exceeded its storage limits. Messages are not resent with this error code because this is usually a sign this is an abandoned email. |
| Error Code 553 |
| Invalid/Inactive user |
| The message was refused because the mailbox name is either malformed or does not exist. Remove these addresses from the list. |
Less Common Error(s):
| Error Code 552 | |
| Mail refused | Delayed Bounce - Unable to Parse Server Reason |
| This is a default response that can be caused by a lot of issues. There is often a more readable portion of this error that gives more detailed information, but, if not, remove the address(es) from the list. | This is what SendGrid displays when the recipient's server returns a blank reason code. |
Keep in mind that this is only a short rundown of the most common errors and a quick definition of why these bounces happen
This guide on How to Unblock an Email Address From the Okta Email Address Bounce List via API may provide a better understanding on these errors and how they can be prevented.
