After migration of exchange server all sent emails apear in the administator postbox

Question

We migrated our Exchange 2010 server to Exchange 2016.

Now we recognize that all emails sent from any account and sent to any account is duplicated into our administrator postbox.

If I send an email from my account [e-mail] this email appears in my postbox and in the admin postbox.

In the admin postbox it is shown as "sent on behalf of". The email itself is attached as an attachment. It doesn't matter if the receiver is inside our domain or external.

Also all inbound email appears in my postbox and in the Admin mailbox.

We have no rules defined at all. Where should I look for the settings that causes this effect?

Further information to my problem:

I checked the mail headers and i found the entry:

X-MS-Exchange-Generated-Message-Source: Journal Agent

I checked Get-JournalRule but it is empty.

Answer 1

I found the problem. It isn't only possible to define journal rules. It is possible to define a Journal receipient also on the data base.

[PS] C:\Windows\system32>Get-MailboxDatabase "mailbox database 2016" | fl *journ*
JournalRecipient : mydom.loc/Group/Users/GroupAgain/Administrator

I found the Setting also in the Management tool for the database. After Clearing it no more emails are sent as a duplicate to my Admin Mailbox.