If some emails that are being restored already exist in the user's / destination account's Mailbox, these emails will be skipped in the restore process. I.e. we don't overwrite the already existing emails. This makes the restore process faster.
OneDrive & SharePoint
Similarly, if an OneDrive or SharePoint file already exists at the time of restoration, these files will be skipped in the restore process.
However, if OneDrive or SharePoint already has an older version of the file, a new file version with the version date included in the filename will be created during the restore process.
If OneDrive or SharePoint has a newer version of the file and an older version is restored, the older version will replace the newer one.
Calendar & Contacts
When calendar entries or contacts are being restored, any already existing entries are overwritten in Microsoft 365.