The Lookup Transform does as the name suggests, it allows us to look up another value in another data location based on a value(s) in the incoming data from an upstream component. The problem being is that the default behaviour is to fail the component if the lookup yielded no matches. This may or may not be what you want. The error you will see is.

 Error: 0xC020901E at Data Flow Task, Lookup [483]: Row yielded no match during lookup.

To stop this happening we need to go into the lookup component and change the error handling by hitting the "Configure Error Output" button on the front screen of the UI. We now have a choice of either ignoring the error or as is the case here we decide to pipe the error to the error output. We think this is a bit of an incorrect usage of the Error Output as the component has not really failed in the true sense of the word but this is the way the component works. Here is how we redirect the output.

To capture the rows that were not matched you simply hook up the error output to a downstream component. Your matched rows will flow down the normal output.