List difference tool

Set operations on two lists: what is in the first only, what is in both, and both combined without duplicates. Separate the lists with a blank line.

Three questions come up constantly with two exports and they are genuinely different: who unsubscribed (in the old list, not the new), who is on both, and the combined mailing list. Doing this in a spreadsheet means VLOOKUP and a column of error values, which works and is more effort than it needs to be. Values are trimmed before comparing, which matters because spreadsheet exports carry trailing spaces that make identical values compare as different. Comparison is exact and case-sensitive — for email addresses, lowercase both lists first with the case converter.