Sorry to start yet another thread on this, but it seemed I could not do a reply on a previous one.
Firstly, I am a novice Mac user, and much of what I read on this subject is over my head. Also, it seems that much of the advice in other posts on this topic is out of date, presumably because Mac OS has changed so much, so that the file structure is no longer the same.
I have the latest version of Yosemite and Lync (updated yesterday).
When I started with this MacBook, I created two users, an admin one and an everyday one. I installed Lync using the everyday user, and it worked. I don't remember exactly how it was set up.
Then I was persuaded I didn't need two users, so I deleted the non-admin one, and reinstalled Lync on the admin account. And I simply cannot get it to sign in.
As far as I can see, email address and User ID should both be the email address associated with my Microsoft account, and the password should be my Microsoft account password (though it doesn't tell you this). So these are all correct.
Now, I have a choice of error messages. If the advanced setting is for automatic configuration, I get the "sign in failed because the service is not available" error. If I change it to manual configuration, using the settings found in various posts, I get "sign in failed because the password is incorrect". It might at least try and be consistent!
I have tried all the suggestions made in previous threads without any success, or they just don't work (I can't find any .cer files, for instance). Why does this have to be so difficult? If anyone can explain in simple terms how to get it running, I would be most grateful!