I have several linked mailboxes, I have to delegate Full control of one mailbox, but it as no effect.
I have try through ECP, adding FC for User alias, no effect.
I have try through Powershell :
Add-MailboxPermission -Identity " TestUser1@accout.com" -User "AccoutCom\TestUser2" -AccessRights FullAccess -InheritanceType All -AutoMapping $false
I have One way forest trust.