Hi Bourne,
I've cleared off the dns cache.
Checking the miis client, i can see its trying to connect to adminwebservice.microsoftonline.com/ProvisioningService.svc, which resolves to 157.55.130.72, however it fails every time with the above errors.
Looking on our firewall logs, I can see the request leaving our network, and it appears to be getting a 500 error back.
"method="CONNECT" srcip="XXX.XXX.XXX.XXX" dstip="157.55.130.72" user="" statuscode="500" cached="0" " size="14646" request="0x9e16828" url="adminwebservice.microsoftonline.com/" exceptions="av,auth,content,url,ssl,certcheck,certdate,mime,cache,fileextension,size" error="Connection reset by peer""
I've checked the account used for sync with O365, and i can successfully login with the credentials that DirSync is using.
The only thing within Miis itself is the "Status: stopped-extension-dll-exception" error, the other errors appear in the event log.
Thanks