The Account Setup is Incorrect: The configuration of the same email account multiple-times can be a cause of repeated synchronization of incoming data, which can cause duplication in the mailbox.

And this, again, leads to data duplication.

The Send/Receive Intervals are Short: Due to the short frequency of the Inbox updates, the email messages, as well as the mailbox components, cannot synchronize properly.

This, in turn, causes data duplication in the Outlook mailbox. Incorrect Outlook Rules: Mistakes cause the rules to be improperly configured.Yes, duplicate emails are a pain, and it can cause a lot of trouble, but how do they end up in your Outlook? What causes this misery? Ever wondered? Here are the causes of duplicate email messages in your Outlook 2016 & 2019: How can You End Up Having Duplicate Emails? Let’s start with knowing the reasons for having duplicate emails in your Outlook. We are going to discuss and work on the same. Ever noticed email duplication in your mailbox of Outlook 2016 or the 2019 version? If you have, you’ll know what we’re talking about! Duplicate emails can be a headache, and hence you’d want to get rid of them, wouldn’t you? Don’t worry, in this blog.

Delete duplicates in outlook folder