

This can be one of the reasons for email duplication in the Outlook mailbox. If the same email account is used in different devices, i.e., laptop and mobile, then it will cause repeated synchronization of the incoming message. If the inbox updates with low frequency, the emails and other data in the mailbox will not get synchronized and will lead to duplication of data. Short intervals in sending and receiving messages.This results in duplication of the emails. If the rules are configured incorrectly, it will create confusion when you receive an email message. The reasons are many, and the possible reasons are listed below. Reasons That Result in Duplication of Email Messages

The Outlook backups will take more space and if you save backups at any external cloud storage, then you will need to pay more for extra space.If the Outlook is configured with Exchange Server or Office 365, duplicate items will increase the size of Exchange/Office 365 mailbox.

It takes more time in accessing new emails and replying to them. It negatively affects the business productivity.
