We have an turst forest between dc.local and exc.local on the dc.local we have a upn @domain.tld and on the Hosted Exchange farm we also have the same domain.tld. Now we have created a linked mailbox to that user but he only can sign in with dc\username
We wants that he also can sign in with firstname.lastname@example.org.
If we create a user on the Hosted Exchange farm it is possible to sign in with the domain.tld but when we created a linked mailbox to dc we only can sign in, in OWA with dc\username
Greets and Thanks