All replicated Symantec Endpoint Protection Managers (SEPM) send the same scheduled report out at the same time. As a result, the email address that is defined will receive a duplicate email for each SEPM that is replicating.
The SEPM replicates the scheduled report with all other replication partners.
This is working as designed. If you do not wish to receive an email from each replication partner then remove the mail server settings from the other SEPM(s).