Came across something odd today.
We use BPOS at AdeoPoint and in general have no issues with the Exchange Online services, today my sign in client could not connect and was showing the error:
“The client was unable to establish a secure connection with the server. Please try signing in again. If the problem persists, please contact your system administrator.”
I look through all of the obvious stuff and ran some general connection tests to make sure we could “see” the remote servers at emea.microsoftonline.com and there appeared to be no issues.
Windows Firewall as off (as is our client PC policy) so nothing obvious presented itself as to being a cause. I’m not much of a Windows client (7 in this case) troubleshooting expert so wrote it off as something transient and pressed on with things sans email.
When using word a while later I inserted a date/time stamp into a document and noticed that the time was wrong. For some reason my PC was an hour out of sync with GMT. I re-sync’d to the time server and lo and behold sign in was able to connect.
A little bit of playing later (change the time; can’t connect, correct the time; can connect) I have now discovered that the time must be pretty accurate on your client PC for sign in to successfully connect to the microsoftonline.com servers.
A small additional security measure I presume.