Is Email Marketer a multithreaded application? If so, how many threads can I create?

Yes, Email Marketer is a multithreaded application. You can use up to 512 threads to send out emails simultaneously in the both Personal or Business Edition. Using multiple threads to send out emails can speed up message sending. However, If you have a large number of threads, it can hurt performance while the OS switches between them, the more threads you have the more memory your app needs.