A collection of raw SMTP error codes spotted in the wild

Find a specific SMTP code or email provider

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What is this?

The SMTP Field Manual is a collection of raw SMTP error code responses from major email service providers and spam filter services. All of the data we’ve collected is open source. Anyone can make contributions, even you! See something interesting from an email service provider or simply have a suggestion? Let us know.

Why we built this →

SMTP Error Codes

4.X.X Persistent transient failure

The mail server encountered a temporary failure. If the command is repeated without any change, it might be completed. Mail servers can use temporary failures like this to keep untrusted senders at bay.

5.X.X permanent error

The mail server has encounted a permanent error. These errors will result in the SMTP connection being dropped. Re-sending will usually produce the same result.

Built with

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