Steam Guard is a great security feature, and it typically works with out a hitch. Recently I reinstalled Steam on my desktop computer to try out the new Humble Indie Bundle that was released earlier this week. Since I have not logged into my Steam account for over a year, a new security feature called Steam Guard prohibited me from logging in without providing a verification code.
This was not a big deal, but for whatever reason, my old Yahoo account that is linked with my Steam account would automatically reject these emails. This appears to be a common bug that Yahoo has not addressed and not a settings or security feature in Yahoo Mail.
Fix Steam Guard verification e-mails In Yahoo Mail simply adding the Steam support email to your contacts list in Yahoo Mail.
If you are still having problems with Steam Guard and Yahoo Mail then please leave us a comment and I will help you research the problem. Also be sure to subscribe to Sultan Solutions Tech Blog, and check back often for updates.