Hi Gavin,
Thanks for your reply. I understand it now. For now, we focus on the problem to rebuild the user " gavin@bizserv.co.za ". First thing, I would like you can create a account named gavin@.onmicrosoft.com ,and also test the autodiscover service on this account. If it works, we are going to the second step, remove the proxy address gavin@bizserv.co.za which have added on Gavin.thompson@bizserv.co.za. After that ,you change the user gavin@.onmicrosoft.com to gavin@bizserv.co.za, and wait for couple hours.
If you have any problem or questions ,please feel free to post them here.
Thanks, Neo Zhu