Due to a recent change made by mail server administrators (including Yahoo), for Domain-based Message Authentication Reporting & Conformance (DMARC) some customers may not receive their order conformation emails.
This is part of a concerted effort to reduce email spoofing (when a sender claims to be sending from an email address they are not actually able to send from). This is generally a malicious practice, and that is why many companies such as Yahoo are taking steps to reduce these behaviors.
More information can be found on our blog post below:
http://yahoomail.tumblr.com/post/82426900353/yahoo-dmarc-policy-change-what-should-senders-do
We apologize for the inconvenience and appreciate your patience while we work toward a suitable resolution for all parties involved.