Assume that you take the following steps to set a forwarding rule in a mail-enabled public folder:
In Outlook, right-click the public folder and then click Properties.
Click Folder Assistant and then click Add Rule.
Select the Forward option, input your email address in the "To" field and select the "Leave Message Intact".
Note All other settings are optional, and don't affect this issue.
After that, when you create a new item in this public folder, you may also receive a copy of it in your Inbox. It's expected that the items that you create should not be forwarded.
This issue occurs because the forwarding rule is triggered wrongly when a new item is created in the public folder.
To resolve this issue, install Cumulative Update 11 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.