Windows
Chrome, Edge and Opera support direct drag and drop of email(s) from Outlook to SharePoint Online / Teams. You can upload multiple emails in a single request.
FireFox requires an intermediate step by saving the email first on the desktop or local disk.
For SharePoint 2019 and SharePoint Server SE the App offers an “Upload email(s)” feature that allows users to upload email(s) from Outlook to SharePoint without intermediate step.
macOS
Safari supports direct drag and drop of email(s) from Outlook to SharePoint / Teams. You can upload multiple emails in a single request.
Chrome, Edge, FireFox and Opera requires users to drag email(s) from Outlook via the local computer to SharePoint / Teams.