SQL - Finding Duplicates Across Columns

I have a table that has 4 e-mail fields. A single contact can have anywhere from 1-4 e-mail addresses on file. I'm having trouble writing a query that displays all duplicates across columns. For my example, I'll only discuss 2 email fields. Example: - John Smith, **Personal Email** fake@fakejohn.com **Work** fake@fakejohn.com - Jane Smith, **Personal Email** jane@fake678.com **Work** NULL - Jane Smith, **Personal Email** NULL **Work** jane@fake678.com In the above example, I can't find a way to say "I have 2 Jane Smiths that are duplicates" because they have the same email, but in different columns *while also* excluding John Smith, because while his email appears twice, I don't want to self-reference, as this is not a duplicate of itself. Iterations of my attempt to find a cross-column duplication check have been unsuccessful but include the following:

Select First, Last, Personal
From Contacts C
where C.Personal = C.Work
  and c.ID  c.ID -- my attempt to prevent self reference

This doesn't work, I receive 0 results, but should have thousands. Without the c.ID c.ID bit, I receive too many results, as I retrieve results for non-duplicate records that simply have the same email address in both fields. I've also added "Group By" clauses based on First & Last name and filter by greater than 1, but when checking our database, I'm still finding that I have contacts with the same name and no e-mail addresses in common *with each other* but have the same scenario as John Smith above. Is there any way to achieve this? I haven't found any queries to get me started.