Changing multiple cells depending on another cell in their row
Solution 1:
Try COUNTIF:
=IF(COUNTIF(List!A:A,A1),"IN","OUT")
Solution 2:
You can do it with MATCH if the Second Sheet is in the same workbook. If it is in a separate workbook, it will still work, but only of the other workbook is open.
=IF( ISNUMBER( MATCH( A2,Sheet2!$A$2:$A$7, 0 ) ), "IN", "OUT" )
Alternatively, if you don't want to do VBA, you can pull the text file into a table in your workbook that is hidden into the data model and then reference it, but that is a long trip and can only be done on an installation that supports Power Query.