Thx Daniel.. I really appreciate your time with this
I'm surprised that Mandrill didn't notify me that they had paused sending, it would have saved many hours of fault finding - how else would I know that they had done this ?
Ok, all test accounts now removed.
I have now set the server mail settings to SMTP for Mandrill and the contact and other site forms are now sending ok. Forum post notifications are now sending - and also UddeIM message notifications.
Thx again Daniel for your help.