table users (old)
-----------------------------------------------------
id  name  emails (removed)
-----------------------------------------------------
1   A     aaa@email.com, bbb@email.com
2   B     ccc@email.com, ddd@email.com, eee@email.com

table user_emails (new table)
---------------------------------
id  user_id  email
---------------------------------
1   1        aaa@email.com
2   1        bbb@email.com
3   2        ccc@email.com
4   2        ddd@email.com
5   2        eee@email.com