This may well be related to how my organisation uses an antiquated version of Exchange, and the fact that I'm using Lync 2011, however, it will not work on macOS Sierra -- starts up, tries to authenticate, then just ceases.
In looking at tcpdump and Console (I like the new Console.app!) there's not a lot of clues given, but, I have the feeling it is related to ATS and the various TLS requirements. Even though I've trusted all the right certificates and whatnot, it won't log in.
Just posting this to make other people's lives easier...