There have been a number of comments on my post about Hotmail moving to SPF authentication having to do with troubleshooting authentication failures. I have been helping clients troubleshoot these issues, and am able to take on new clients to solve authentication problems. Contact me for more information.
Of course, many of these issues can be solved with access to the right tools. Steve’s been working on a number of tools that may help the troubleshooting process and we’ve recently launched them on Emailstuff.org. The website itself contains a number of DNS and data related tools we use for investigations and thought we’d share with the public at large.
One of the really useful tools is the SPF record expander. Plug in any domain, like google.com, and see what IP addresses they authorize to send mail.

This is an approximate list of the IP addresses that the domain google.com allows email to be sent from according to their SPF record
google

64.18.0.0/20
[…]
2a00:1450:4000::/36

The other neat feature is the RFC viewer. We’ve highlighted email related RFCs, but we are mirroring all the RFCs from the IETF.org website.
The DKIM tools are the same as you’ll find on our DKIMcore.org website.
These tools are just in beta, and are still actively in development. If you have any suggestions, comments or improvements you can send them to us. If you have any additional tools you’re interested in please let us know.

DKIM • dns • spf • Tools