Hi @Henn Sarv ,Welcome to our forum!
- Saving Outlook attachments to OneDrive does not directly reduce your mailbox storage space. Your mailbox storage space depends on the number and size of your emails, not the location of the attachments. If you want to save mailbox storage space, you can delete some unnecessary emails or attachments.
- If you have already saved Outlook attachments to OneDrive, you can choose whether to delete the original attachments according to your needs. Deleting the original attachments will not affect the copies in OneDrive, but will reduce your mailbox storage space.
- In classic Outlook, upload to OneDrive is to upload attachments from your local computer to a folder in OneDrive. In modern Outlook or Outlook Web App, save to OneDrive is to directly save the received email attachments to a specific folder in OneDrive (Email attachments from Flow). The difference is that upload to OneDrive requires manual selection of files and folders, while save to OneDrive only needs one-click operation.
- Currently, Outlook does not provide an option to automatically save all attachments to OneDrive, if you want to save existing email attachments in bulk to OneDrive, based on my search, you can use Microsoft Flow to create an automated workflow to achieve that. Please kindly understand here which mainly focus on general issues about Outlook desktop client. It is suggested for you to post a new thread to the dedicated forum via this link for more appropriate help.
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