Incoming mail appears to be working OK: POP clients such as Windows Live Mail and Thunderbird are picking up up new messages immediately. and incoming mail from other addresses (eg my Gmail address) are being delivered very promptly to the server from which I can download them by POP. Webmail is a bit slow but seems to be working.
However outgoing mail by SMTP is not working: various test messages never get sent - "server has disconnected".
That's the situation now at 10:00.
So there is still a problem, but less severe.