Download Email as Attachment
Because Outlook Web is a browser-based email viewer, you cannot use it to create a backup PST file. However, you can download and store the emails that you want to keep by attaching them to a New Email Message and then download it to your local or OneDrive folder.
1. Open a NEW MESSAGE
2. Click on the "Box and Arrow" icon on the top right corner of the new email message to open it in a new window
3. Select the emails that you want to download by clicking on the circle to the right of the email
4. Drag the selected emails to your NEW MESSAGE email
5. When the emails have been attached, click on the download arrow 
or the V to download it to your local or OneDrive folder for storage.
