Hello @Dipika Bhamare ,
Welcome to Q&A Forum!
According to my research, we cannot open directly to view .msg files in SharePoint Online. We need to download the .msg file and open it in Outlook. It is by design.
In new UI (modern mode), when previewing .msg file in the browser, there’s no way to view the. In the classic SharePoint library is also a download behavior. When you click the email files' Document ID, the pop-up window indicates that the email files have been downloaded automatically and then you can open the files in the Outlook client. So, whether in the modern view or the classic view, the .msg file and .oft will not be opened in Outlook Web App. We need to download them and then open them in Outlook.
Thanks,
Echo Du
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