Linking a previous M365 to current one

Microsoft 365 subscriptions and personal Microsoft accounts cannot be merged, and a subscription cannot be transferred from one Microsoft account to another.

If the old storage is in a different personal Microsoft account, the practical path is:

1. Sign in to the old account at https://onedrive.com and check whether the old files are still there.
2. If the files are available, download the files that need to be kept.
3. Sign in to the current account and upload those files to the current OneDrive.
4. Keep in mind that when a Microsoft 365 subscription is canceled or expires, access to the included OneDrive storage is affected, so copying out important files before closing or abandoning the old account is important.

If the old and new sign-in use the same email identity in Outlook, linking can apply to subscription features in new Outlook for certain third-party email accounts, but that does not merge accounts or move old OneDrive storage between accounts.

If the sign-in prompt shows both a personal account and a work or school account with the same email address, those also cannot be merged. They can only be used side by side.

References:

• Which account do you want to use? | Microsoft Support
• Link non-Microsoft email accounts to your existing Microsoft subscription | Microsoft Support
• Why did I get a message saying my files will be erased? | Microsoft Support
• Move Subscription from one email account to a different one - Microsoft Q&A
• How do I merge 2 M365 family subscriptions into 1 - Microsoft Q&A