This is only relevant if you have turned on sync emails from Microsoft Office 365.
If you delete an email in Microsoft Outlook Microsoft will classify that as a new event and notify Salesbox that there is a new email to fetch. If that email was not synced earlier (older than the time you turned on the sync between Salesbox and Office 365) then it will be added to the Latest communication on the corresponding contact in Salesbox.
The date/time of that email will be the date/time shared by Microsoft, which is the date/time for when the delete action in Outlook occurred. If you do not want this email in Salesbox you can always delete it by clicking the X button to the right of the email in Latest communication in Salesbox.