We have a hybrid setup, no problems with email communications between on-premises and Microsoft Online users. We have also activated online Onedrive/sharepoint to start testing. One interesting thing is that users Online can share their documents by inviting users who are on Microsoft Online, On-premises and outside this two systems. But the problem is with the users who are on-premises cannot share their documents by email invitation with the other users who are also on-premises, they can share the documents with the users who are online only. When they try to share documents by email invitation they get error messages it their emailboxes saying that;
A communication failure occurred during the delivery of this message. Please try resending the message later. If the problem continues, contact your helpdesk.
Generating server: SMT947322-001.YLO001.MSOPRD.MSFT.NET
#< #5.5.0 smtp;550 Denied by policy> #SMTP#
It seems some kind of relay should be granted on my CAS servers or something like that but I am not sure of what should be added. I am just stuck as to what next step and where to start looking for the problem
Exchange 2010/2013 with Microsoft Online Office 365 Hybrid