Email account list reconciliation

We have two different lists of email addresses. The first list is in Column A and the second list of email addresses is in column B.

I'd like to set up a function that would list all email addresses in column C that are listed in column A and are not listed in column B.

Another function that lists all email addresses in column D that are listed in column B that are not in column A.

We have two user databases here and need to reconcile a list of users. These two functions will leave us with a list of only active employees.

Any tips?