Make sure the network connection which you are using is stable. If the connection is slow or there is latency in the network, Outlook Add-ons won’t work properly. Avoid downloading heavy files while using Outlook.com especially files via torrent client. These clients consume all the bandwidth as a result, Outlook doesn’t work perfectly fine. If you aren’t able to attach any file, most of the time it is due to the bad connection so make sure that the connection you are using is fast and stable with zero latency. Contact your network administrator or call your internet service provider for help in case you are facing connection issue. For feel free contact us Outlook customer service support for regarding any questions, answers to account.