This one's got me a bit stumped.

One user at one of our client companies cannot send some of her email. When she attempts, she gets this message:

"You do not have permission to send to this recepient. For assistance, contact your system administrator.
MSEXCH:MSExchangeIS:/DC=com/DC=domain:ExchangeServer"

Where "domain" is the domain name and "ExchangeServer" is the name of the server running Exchange.