v7.1 Exchange Synchronization: set "send as" permission on Mailbox


I have a question regarding Exchange and the "send as" permission on a Mailbox (EX0Mailbox).

All of my new created mailboxes looking good, but the "send as" field is empty.

How can I easily set the "send as" permission on a mailbox?

I already figured out the "send on behalf" permission for other users, but didn't found the configuration for the "send as" permission. 

Thanks, Fatih