I got the same problem!!!
I search 3 days internet but still no answer to found out!
finally,I try to adjust every setting in my laptop,thank god!!!I found out
the problem!!It cause by Norton!!!! Inside norton or other anti-virus
software,click option or setting then look for " how to keep Microsoft Office
Document protected " uncheck or unclick " Turn on scanning for Microsoft
Office documents " then the probelm its gone right away,when I open again
Windows mail no more problem and very fast too
hopw this can help you!