An odd one, the client PC(Windows 10 Creators Update) presented mainly with Outlook connecting very slowly to exchange, thereafter it was almost unusable. It would hang on trying to send and email and updating the folders were slow to non-existent.
It appeared that some https websites were very slow to respond as well, sometimes not loading at all. The smartscreen filter also was non functional ("Smartscreen filter can't be reached now")
Try the following DNS change in group policy. Run gpedit.msc, under Computer configuration -> Administrative Templates -> Network -> DNS Client: Set "Turn off smart multi-homed name resolution" to Enabled.
Note1: You may need to untick IPV6 under network adapters in case this fix does not work. Note, some testing is still needed to isolate this as the root cause.
Note2: The assumption is that the usual suspects have been eliminated, ie, Office repair/reinstall, network reset, file integrity checks [sfc /scannow], virus/malware checks, new office profile, new windows profile etc
