Access shared mailbox in a cross forest deployment

Hi all,

We had a cross-forest Exchange migration (2010 => 2013) last weekend and now we've trouble with a shared mailbox:

I try to connect a shared mailbox from the resource forest to an Outlook (2010) client in the user forest. The user has no linked mailbox, but fullaccess permission for the shared mailbox.

When I set up the email profile Outlook says it can't find the name in the addresslist.

(Mailbox isn't hidden from addresslist).

Thanks,

Jonas