Host Not Reachable errors today from all types of email

Host Not Reachable errors today from all types of email

Hi there. Of course I'm on a deadline. I'm suddenly getting "Host Not Reachable" Error 421 on emails. Is this a system problem over at Zoho or is there something I am doing wrong? One of them is my publisher. I must be able to work with him to finish up a magazine this week.

Maybe this is just part of all the cyber attack stuff I keep hearing about?