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What is SMTP Field Manual?
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.
![SMTP Field Manual media 1](https://ph-files.imgix.net/1e934716-a892-4b94-b513-1177bc4d56f2.png?auto=compress&codec=mozjpeg&cs=strip&auto=format&w=256&h=160&fit=crop)
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![SMTP Field Manual media 3](https://ph-files.imgix.net/d9d9c34a-ecc3-4a63-bdf8-0298592a6aea.png?auto=compress&codec=mozjpeg&cs=strip&auto=format&w=256&h=160&fit=crop)
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SMTP Field Manual
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.
![SMTP Field Manual image](https://ph-files.imgix.net/1e934716-a892-4b94-b513-1177bc4d56f2.png?auto=compress&codec=mozjpeg&cs=strip&auto=format&w=150&h=90&fit=crop)