On April 4th, 2014 Yahoo.com implemented a change to their email system linked to a policy titled DMARC.
DMARC stands for Domain-based Message Authentication, Reporting & Conformance and it is an email authentication policy that aims to prevent spoofing and spamming linked to the"From" email address on messages.

The change in this policy implemented by Yahoo means that any email message using a "From" email address of @yahoo.com must originate from Yahoo's own email servers. Messages sent through any application outside of Yahoo itself, with a From address of @yahoo.com will be rejected. These affected applications include ACTIVE Works® Camps and Class Manager. (or other ACTIVE Network applications)

To prevent future email messages from being rejected, please update your confirmation email, and broadcast email From settings to a different email address, other than Yahoo. Please refer to the instructions below to enable those updates.

To Update Your Confirmation Email:

  1. Click Edit Setup under season name
  2. Navigate to Confirmation Email step
  3. Update FROM email address
  4. Save and Continue

To Update Broadcast Email From Email Address:

  1. Navigate to Emails tab
  2. Click New > New email
  3. Update FROM email address
  4. Save