I'm in the process of trying to integrate our CUC with Office365, when I setup my user account and tried testing, I received a 503 error, I've included a screenshot. Wondering has anyone encountered this as well, and also suggestions on how I can resolve this issue. We're running CUC 8.6.2ES44.22900-44
Support for Office 365 Wave 15 comes with CUC 8.6(2) ES 73. The version you are on does not support Office 365.
Apart from this, as Terry mentioned, there is another issue with IPv6. I don't have information about the exact fixed version but it should be supported in the later ESs. You can go to the latest SU available on CCO.