SMTP Field Manual: A collection of SMTP error codes from major inbox providers.

Hey everyone. We've been sending email (as an email service provider) for nearly 16 years at Wildbit. Arguably the most confusing aspects of email delivery is bounce management and SMTP response codes. If you're unfamiliar, ISPs (like Gmail, Office 365) will send SMTP responses back about the success or failure of the messages you send. To bring more clarity and accuracy to SMTP responses, we just launched the SMTP Field Manual to be a free, one-stop resource for understanding all SMTP error codes from all the major inbox providers. We hope this becomes a valuable resource for anyone who relies on email delivery. Please help us spread the word (and contribute!) to make it even more valuable.