We are currently seeing delivery problems for email messages destined to Mimecast in Sout Africa. The typical response is “451 Open relay not allowed”. At this time the mimecast.co.za website redirect to mimecast.com is also not responding, suggesting that Mimecast is experiencing technical issues.
Mimecast is a first-class email service. Many companies rely on them for secure email, filtering of undesirable content, and message archiving. It seems even the greats sometime stumble.
Our mail servers will continue retry messages that are queued for delivery to Mimecast. For now, there is nothing you or we can do to solve the problem other than wait.