Qmail: Routing outgoing SMTP through smarthost
If, like me, you are still using an old style LAMP stack combining Web and E-Mail, then you certainly made a “stay over” in SPAM-paradise. The Stack I self-host my E-Mails, using QMail and vpopmail with a bunch of intermediate tools like Spamassassin, Clamav, Greylisting, DNSBL checks. This helps to clean out incoming SPAM. Messages are delivered to users through courier-imap or qmail-pop3d. For outgoing messages, Qmail sends (via qmail-remote) the messages via SMTP to the concerned MX servers.