Protoport Sendmail Server Description:

Powerful direct remailer software actr as SMTP relay. It puts email messages directly to mailbox of recipient. ISP's SMTP server is not involved. The program will query DNS for MX records, and deliver emails to so-called mail exhange servers. This is much more faster and more reliable. You can even use HTTP proxy server for sending emails. This is useful if you are behind corporate firewall, for example.