Someone else had same error code before, and it was caused by not having the right "your own email address" when setting up the account.
This address is used as the sender (From header) and Exchange gets unhappy if it isn't what it expects.
So please check that, long press the account -> account setup.
Can happen if for example your "real" email address, as far as Exchange is concerned, is, say, "john.smith@corp.com" but there is an alias say "john.s@corp.com". If the alias doesn't have the "rights" to send mail (as the account itself does), then Exchange won't allow sending.
