cannot send as or send on behalf of mailbox in outlook

cannot send as or send on behalf of mailbox in outlook

The issues was cause because the email address in the outlook offline address book did not match the email address in the portal. To fix this follow these steps:
1/ open outlook
2/ click the send and receive tab
3/ click send and receive groups
4/ click download address book
5/ uncheck download address book since last changes
6/ click OK
7/ when complete try to add the address again to the from field now that it matches.