So what do you do when you have tens of thousands of customers around the world who are used to using their domain’s smtp server without any smtp authentication? Well, if it wasn’t for spammers, you would let them keep on doing it. But, unfortunately, spammers just never stop. They are constantly scanning for any kind of hole that they can find. Some days I really hate spammers, they can ruin your day. As a system administrator, mail is a common maintenance task. I’ve worked with many types of mail servers: Imail, sendmail, postfix, and qmail. So far postfix is my favorite and I highly recommend using MailScanner for a complete package of software for spam and anti-virus protection on your server. I’m still looking for a better solution then qmail for multiple domain e-mail hosting, but hope to someday have time to look into dovecot and cyrus. Before postfix, I used to evangelize sendmail, but over the years I have realized there is an easier way (and works better too).