Yahoo Email Servers are Down for quite sometime
We are observing a global level problems in delivering emails to Yahoo users because of certain email acceptance issues on Yahoo servers.
Lots of ESPs are taking about the same but till now no official updates from yahoo or any other ESPs.
For more details, Refer: http://downrightnow.com/yahoomail
Due to this temporary issue you may experience delay in email campaigns delivery. Our Delivery experts team is continuously monitoring this and trying to minimise the impact.
We will keep you posted with further updates on the same.