How to use the bounce decoder tool

I've added a few tools to this site, partially as quick access for myself, but also in the hope that you might also find them useful!

Today's tool is the bounce decoder. If you've ever looked through your email service provider's logs and spotted a failure, you may have noticed the 4.X.X or 5.X.X number alongside it. These failure codes describe the reason your email bounced. There's a message attached to the code too, and for all major ESPs these are heavily customised. That means you don't just have to learn to interpret these messages once, but you need a whole language to deal with the different bounce messages.

With this tool, you can paste in the bounce message from any major ESP for a real breakdown of what it means, making it much easier to identify the cause. For smaller ESPs, the tool just grabs the more complete description of the bounce based on the standard code.

If you've worked out why your emails are bouncing, but you're not sure what to do next...