Cool tool: SMTP Codes

Here's a simple-but-cool tool created by Faisal Misle: smtp.codes.

smtp.codes is a collection of SMTP response codes returned by email servers and a guide to help you understand what the SMTP codes that various email servers respond with mean.

In short, it's a library of example bounces; SMTP rejections and deferrals. What mailbox providers say back to you when delivery is delayed or denied.

There have been other efforts like this in the past, but one of the more well-known ones has seemingly stopped updating, so Faisal kindly stepped in to create an updated resource, where we can share our examples and feedback to help keep it up to date.

You can find it at the web address https://smtp.codes

Thanks, Faisal!