From OCloud Software:
Mail Direct is a program that will allow you bypass your ISP's mail server and use your computer to send e-mails directly to recipients. The program can do this because it has a built-in SMTP server which you can use instead of your ISP's mail server. All you have to do is set up your e-mail client to use 'localhost' as your outgoing mail server and run Mail Direct. The program will then deliver any e-mail that you send out through it, and it will terminate delivery of messages that you have sent out to wrong or bad e-mail addresses.