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
If a OneDrive or SharePoint file with the same timestamp already exists at the time of restore, that file will be skipped during the restore process.
If OneDrive or SharePoint contains a file with the same name but a different timestamp, the restored file will replace the existing version.
Calendar & Contacts
When calendar entries or contacts are being restored, any already existing entries are overwritten in Microsoft 365.