More and more emails are being blocked by hard bounce with valid email addresses

We’ve seen an increase in customers reporting they are no longer receiving emails from us. This is across all providers.

We’re seeing a lot more that Keap reports as a hard bounce. However when our customer service team emails them from outside of Keap the emails arrive just fine. Same thing for emails from our external marketing software.

I know there was an issue with Yahoo last spring. Does anyone know if there’s any email challenges lately with Keap’s email system?

There’s this post from February but no response to it: Not being able to unblock valid email hard bounce Customers