You're not the only one having this problem with Exchange servers. Every so often, Mail gets stuck on that spinning wheel you describe, but it only occurs on the Exchange server account. All other accounts that I have check and receive mail flawlessly. The spinning wheel doesn't seem to affect incoming mail; even though the spinning wheel gives the appearance that it's hung up, new mail still arrives. It's just more of an annoyance to me, so I quit Mail and immediately re-open it and the spinning stops (for awhile). Face it. Macs still hating talking to Microsoft devices. I think that's the bottom line explanation.