Not sure who this may help but my solution to this issue was not what I had expected in order to get my MS Exchange to work.

Anyway, the IT dept gave m all the info to log on, etc but I was not successful. I kept getting a message saying "Certificate not trusted" or something. So what I did was I went to my browser and I opened up my company's web-based email. From there, the browser will ask you if you want to trust this certificate. Click on the "Trust Certificate". Do not click "Trust once". Once you've done this, go back to your email client and try to set everything up once again. You should be able to bypass that error message.