Exchange 2013 cu21, Windows Server 2008 R2 domain
this has happened before with the administrator account so i was forced to find a work around.
i created a shared mailbox, delegated users who can "send as" as well as have "full access" to the mailbox. worked fine for many months. until today.
all of a sudden no one can send on behalf of the shared mailbox account. checking here and there, someone suggested to try the administrator account again. well what do you know, it worked again! we were able to send on behalf of the administrator account again.
question is, what is happening? how to resolve this permanently?