Lookup Fail - Error Handling

HI, 
Is it possible when lookup fails to write down the 'failed lookup' to log file or to a text file of some sorts which I can then send for further processing?

Case in point
1. List of client names we have is their registered company for example Koton MagazaclikTeksil San Ve Tic A.S 
2. We have a CSV file where we've saved it's short named with simply Koton
3. When lookups fails , we wish to compile this list 'somewhere' so we can review it , let's say I email this
4. Currently I dont' know how to do this see write 'message to file' and set package variable but don't know how to use this

Lookup is a transformation function,
if you want to validate the data you have to to use appropriate validation function inside the validator