I spent the whole day today stepping through DomainKeys, DKIM, and SPF for a customer to make sure that they were all set up and working properly. I found a couple of the existing tools available on the Internet didn’t test them properly and didn’t give enough explanation when they failed.
So, I went about creating some of my own tests using a bunch of Perl modules. I finally fixed a couple issues that I think were causing problems for this customer. Gmail and Yahoo are now delivering the messages anyway. Hotmail is still a mystery (no surprise since its from Microsoft). Their troubleshooting website is full of talk about how great their service is, but there is a huge lack of anything technical on the site.
Anyway, I made all of these nifty testers and figured that others might like to use them. So I created a way for others to send mail to it, and a web interface that you can view all of them results. I’ve added it as a link to the top of my website.