Our MySQL database is having only 1 table for "member". If we import 10 emails in List1, then follow by 100 emails to List2, all 110 emails will be added to same "member" table. So, we need to have multiple table for List1 and List2, etc... rather than all dumped into only 1 single "member" table. When our user create a new mail list in our software, then MySQL will automatically create new a table for new mail list.
Reason why is, our software will take a very high load (memory usage) to read whole database even if you just send to a small mail list. By separating the mail list to different table, our software will only read selected table only.