We manage a few tenants for our customers, but one of them has a weird issue regarding saving attachment to Sharepoint. Problem is only with Outlook, they usualy right click an attachment, save as and save it directly into a Sharepoint Library (so not a OneDrive folder). It doesn't give any error message (neither in the eventvwr) but it doesn't actually store the file in Sharepoint.
Doing the exact same steps from Word, this works just fine. Also connecting the Sharepoint library through webdav as a disk works fine.
We tried with Outlook 2016 version 16.0.10228 and 16.0.8431
Doing the same steps in another tenant works also just fine.
We recently activated Cloud App Security for this tenant but I cannot see how this is related (but just mentioning it to be sure).
Hopefully someone has an idea, it's not a big issue but some people are used to working this way.