Hi mohamed,
Thank you for your question.
If we want to test message flow in internal, we could do nothing after Exchange installation completed. The link which you provide is about external message flow.
We must restart Exchange server after installation completed, In order to test internal message flow, we could create two test account, then make sure all necessary services are running, we could also restart Microsoft Exchange Transport services on Exchange
to check if the issue persist.
We could refresh the OWA to check if the issue persist, we could logon with recipient account to check if the email was received.
If there are any questions regarding this issue, please be free to let me know.
Best Regard,
Jim