SMTP Field Manual
A collection of SMTP error codes from major inbox providers.
SMTP Field Manual launched on November 5, 2019 with 49 votes, #682 of 3,203 launches that month and more than 50% of that year's launches. The site was still online in September 2026, 6 years on.
What it does
To bring more clarity and accuracy to SMTP responses, Postmark presents the SMTP Field Manual, a one-stop resource for understanding SMTP error codes from all the major inbox providers and spam filter services.
A collection of raw SMTP error responses from major email service providers and spam filters.
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 . 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. The mail server has encounted a permanent error. These errors will result in the SMTP connection being dropped. Re-sending will usually produce the samefrom smtpfieldmanual.com
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