Accepted domain onnprem Exchange and EXO




our customer has primary domain ( with Exchange 2016 Hybrid. 

Later they bought a new domain (, added to O365 and configured some mailboxes wih domain. These are cloud-only mailboxes. This domain is not added to onprem Exchange accepted domain.


Is there any risk if I add this domain to onprem Exchange accepted domain? (for example, existing cloud-only mailboxes will be deleted or something problematic thing?)


Thank you,


2 Replies
best response confirmed by IstvanffyZ (Contributor)
No, no risk. Though if you do plan to use the domain for on-premises recipients as well, it's best to rerun the HCW after you've added it.
Thank you Vasil, I'll check it.