I’m having the same problem. Suddenly seeing the 503 Service unavailable and not subscriber list is not getting updated from wordpress forms.
I ran the curl command on the server “curl -v https://us1.api.mailchimp.com/3.0/?apikey=test” modifying the US1 and Test with info from my MC key and the connection was successful. So doesnt seem like i was blocked by Akamai. Can someone respond to this ASAP?