Duplicate Emails in Archive
If you find that duplicate emails are appearing in the archive then this is most likely related to journaling being incorrectly configured.
The correct configuration of journaling will be configured for internal email only. If it is configured for all email then any email that is inbound from an external sender or outbound to external recipients will result in a duplicated entry being added to the archive.
The happens because the Unique ID (UID) associated with the email is overridden when a journaling envelope is created. The envelope contains additional data added by the email system. Because the UID is different from the original email UID the Mailsphere archive treats it as a unique email even though it is actually a duplicate.
Resolution: If you are experiencing duplicate emails in the archive please check the Exchange Configuration article and ensure that your journaling rules for your version of MS Exchange are correctly set up.