- Review the settings of the client or device
Check the settings of the email client or device that is used to send mail, to ensure that duplicate copies of the email are not created. - Check for the rule causing duplicates
Check Rules folders in the email client or device to ensure that there is no rule configured to make copies of the sent mails. - Disable the cached mode
The cached mode feature creates a local copy of the Exchange mailbox information, so it is recommended to disable this feature. - Change the delivery option
Change the delivery option in Outlook to Send Immediately instead of the default option, Defer Delivery.
