Using Outlook for iOS for personal email and calendar management
Hello
Unfortunately, you cannot separate OneDrive storage from your Outlook.com account. Both services are linked to the same Microsoft account and share the 5 GB Microsoft cloud storage quota.
Microsoft actually has two separate storage limits:
15 GB for Outlook.com email storage
5 GB for Microsoft cloud storage, which includes OneDrive files, photos, and Outlook.com attachments.
Even though you are only using 634 MB of your 15 GB email storage, if your 5 GB cloud storage is full, Outlook.com may stop sending and receiving emails.
Microsoft explains this here:
https://support.microsoft.com/en-us/outlook/storage-limits-in-outlook-com (See screenshot below)
"Attachments in outlook.com" is the key phrase here.
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To resolve this without purchasing additional storage, you would need to free up space in OneDrive.
Go to https://onedrive.live.com/ and sign in with the same Microsoft account.
Review your files and photos, particularly the larger ones.
Download any files you want to keep to your computer first, then delete them from OneDrive.
Open the OneDrive Recycle Bin and empty it to permanently free up the storage space. Updated space can take up to 48 hours to reflect in your account.
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Please be careful if you have OneDrive syncing with your computer, as deleting files from OneDrive can also remove them from your synced folders. So, only delete the files that you asbolutely don't need.