Allow Users from Trusted Domain to access Shared Mailboxes

As this is not possible to do with the Exchange 2010 GUI, here the two Exchange – Powershell commands needed

To add FullAccess rights to an trusted account:

[PS] C:>Add-MailboxPermission -Identity <> -User <trusted_domain><user> -AccessRights FullAccess -InheritanceType All

To add “Send-As” Rights, you will have to change the AD – Permissions for the account:

[PS] C:>Add-ADPermission -Identity ‘CN=Shared Mailbox Name,OU=users,DC=domain,DC=com’ -User <trusted_domain><user> -ExtendedRights ‘Send-as’

to be on the safe side, add the shared mailbox in LDAP notation