The Reason for Yahoo Hard Bounces in Mailchimp

I’ve been working with a client recently that suddenly started to get large numbers of hard bounces from the email campaigns she sent from Mailchimp.

I thought I’d share the reason for this as it may assist others.

The client in question sends email campaigns regularly to tens of thousands of recipients. Her open and click rates are very high for her industry. Over the years she has used Mailchimp her hard bounce rates have been very typical and constant.

It was odd therefore when she advised me how the hard bounce rates had jumped significantly.

Diagnosing Hard Bounce Errors in Mailchimp

Mailchimp makes available the “bounce reason”. Although it can be a bit tricky to understand if you’re not used to it, many of the hard bounces in the clients account had the following diagnostic information:

554 delivery error: dd Sorry, your message to *****@yahoo.com cannot be delivered. This mailbox is disabled (554.30)

That the mailbox is disabled is a perfectly good reason for a hard bounce. When looking at the email addresses in the list of bounced email addresses in the Mailchimp report for a campaign it was immediately obvious that the majority of email addresses that hard bounced were Yahoo email addresses.

Why Yahoo Email Addresses Suddenly Hard Bounce

After a bit of research the reason for the Yahoo email addresses hard bouncing become obvious; Yahoo occasionally disable email addresses that haven’t been signed-in to for 12 months or more.