Manuals are your friends.
Read the mysql manual about JOIN statements.
You are really just a few chars away from a working statement.
SELECT email from table1 WHERE table2.id == table1.id
should be:
SELECT email from table1,table2 WHERE table2.id = table1.id;
note the single "=" statement.
If you also have an "email" field in your table2, you must identify which of the two email fields you want to get: "table1.email"