We had the exact same thing for a particular campaign we sent on Friday 4th March. 20% bounce rate which has never happened before.

I heard back from Klaviyos team and they said there was issues with Verizon Media Group (the parent company for Yahoo / AOL inboxes) regarding issues with their reception of the email stream. They said it was fixed and I re-sent my campaign to the bounced emails and they all went through perfectly. Maybe give it another try? 

Hi there @kr_innox and @ngarza,

Thank you for sharing that information. You are correct that on March 4th, we recently identified some cases of elevated bounces affecting Yahoo and AOL inboxes. Our teams have worked to resolve this issue with reception of the email stream for select providers, so you shouldn't find the issue anymore. You can now send emails to those profiles again without seeing elevated bounce rates. 

However, if you are seeing a 20% bounce rate occur again please let me know.

Thank you!
Alex
 

We just had a same issue with bounced emails from yahoo and aol acounts.

Bounce rate went up to 30% and I see that most of the bounced emails are aol and yahoo. 

Any solution??