Transport rule exceptions look very similar to transport rule conditions. Transport rule conditions are used to identify which messages are to have the transport rule action applied to them; however, exceptions are used to exclude specific messages from the transport rule action. Exceptions are essentially loopholes in the transport rule, overriding the conditions and preventing a transport rule action from being applied to an e-mail message. You can configure multiple exceptions in a given transport rule, and it is important to understand that the logical relationship of these exceptions is such that if any one of the exceptions evaluates as true, then the message bypasses the rule - even if all of the conditions are met. To further explain the logical relationships in a transport rule.
More info: Transport Rules: Exception to the Rule