In outlook i am logged in as cloud user and From Tab i have selected onprem user. When i try to send i am getting below error
Your message did not reach some or all of the intended recipients.
Subject: TEST Sent: 05-Oct-18 2:00 PM
The following recipient(s) cannot be reached:
firstname.lastname@example.org on 05-Oct-18 2:00 PM This message could not be sent. Try sending the message again later, or contact your network administrator. You do not have the permission to send the message on behalf of the specified user. Error is [0x80070005-0x0004dc-0x000524].
I can tell you cross-premises permissions are one of the more difficult and challenging things to get working in an O365 hybrid deployment. So I wish you the best on your journey to find this one out.
Here are a list of things to check
1. First, check the remote mailbox object on-prem. Is it created correctly, is the target delivery address correct? This is the first step in ensuring everything moves on correctly.
2. Check the connectors. I assume you set them up using the Hybrid Configuration Wizard. Think of running through it again. They need to be setup and working properly, allowing communication to flow through, and for that communication to be seen as internal.
Start there, I would think one of those steps will lead to the issue, which at first glance im guessing is the delegates not writing back. Trying to add that manually, or trying another permissions should give you an idea.