Laura Atkins over at the Word to the Wise blog posted an interesting article on undocumented changes that seem to have taken place behind the scenes at Yahoo Mail.  Multiple sources are reporting an increase in “invalid user” or hard bounces at Yahoo over the last couple of weeks.  It appears that Yahoo is not only revamping their email client interface but is now hard bouncing dormant addresses that were recently accepting mail.  Although there is no official documentation of this, it appears that mailboxes that have been dormant for 6 months are no longer accepting mail.

Throughout the SocketLabs On-Demand SMTP service we are seeing an increase in Yahoo hard bounces.  Customers who do not routinely clean their list of unengaged addresses will be affected the most with these recent changes.  An increase in hard bounces at any ISP can have an overall negative effect on your deliverability at that ISP.  Given this latest change at Yahoo it is recommended that all customers take a close look at their list engagement and make adjustments to their lists so that delivery to engaged addresses is not affected. We also recommend that you clean your list of these latest invalid address bounces.

A sample error code would appear similar to: “554 delivery error: dd Sorry your message to [email protected] cannot be delivered. This account has been disabled or discontinued.”

Because of our Suppression List technology we are preventing subsequent delivery attempts to these bounced addresses, but all email delivery requests sent through SocketLabs count against your monthly plan volume so we highly recommend removing suppressed addresses from your list(s).