Yahoo PH01 Block — Email Bounces to Yahoo/AOL Recipients

Incident Report for Klaviyo

Resolved

The block within the Yahoo infrastructure that resulted in these elevated bounces has been resolved. Customers can safely resend to bounced recipients from this time period. This incident has been resolved.

Posted Jul 02, 2026 - 10:17 EDT

Investigating

Starting at 02:30AM US/Eastern on 07/02/2026, a subset of customers are currently experiencing an increase in bounced emails to Yahoo and AOL recipients with the reason of "554 Message not allowed - [PH01] Email not accepted for policy reasons.".

Our Engineering and Deliverability teams are actively investigating and working with Yahoo to resolve the issue. We do not recommend resending to those bounced recipients at this moment in time.

Posted Jul 02, 2026 - 08:17 EDT

This incident affected: Email Sending (Email Deliverability).