I have two tables. One has subscribers to the first three issues of my magazine, the other has subscribers to the next three issues of my magazine.
That isn't a design that makes a lot of sense. It would be better to use one table for all subscribers linked to a table of all subscriptions.
But working from your current design, If you define a relationship linking the tables by email address, you can put the email address field from table 1 on your table 2 layout, enter find mode, put a single asterisk (*) into that field, select the Omit button and perform your find.