Yahoo changed their DMARC policy
They have added “p=reject” DMARC record into yahoo.com domain. Basically, all messages sending from an email with yahoo.com, but not from Yahoo’s servers, will be bounced.
While this policy can help Yahoo reducing amount of phishing emails from yahoo.com domain, it might bring trouble to website owners when they are utilizing online contact form. Imagine this:
Your website has a contact form. It has a field for user filling out their email. Customer A puts his email aaaa@yahoo.com into it. Many forms right now takes value of that field as the sender email. So, the message will have sender as A<aaaa@yahoo.com>.
The result is that that email message will be bounced. And you will not know about it.
How to fix
Unfortunately, we cannot force Yahoo change their rules. In fact, it’s a good policy. What we can do is working around the form. Instead of using value in email field directly, you should replace it by another email with your own domain. Then capture customer’s email to message body.
Depending on each contact form which you are using, the change can be a bit different. However, it is not a hard task. It should not take more than 5 minutes for applying, either with WordPress-based form or custom code. Contact us if you need help on this.