The following are possible causes:
1. Email is being sent from a refreshed environment, where the mail server is enabled and the refreshed environment contains recipient email.
Upon restoration, the mail server continues to do its job of sending email to the recipient.
2. A custom process running a custom GEL script is ran to send end users having timesheet status or hours meeting a certain criteria, e.g. timesheet is still open or submitted and/or having less than X amount of hours for a given time period.