"Taking full control of your own email, that is running your own
email server, is a must if you really care about privacy, security
or maximum customization.
"When you start doing it though, you soon find out that the
hardest, or at least lest documented task, is not how to send
email, or how to block spam. It is how to make sure that the email
you send is always accepted by other sites, that is how to find out
if your email server looks like a spam source.
"Here is a list of tips that I used to check this part of my
configuration. I got them from a thread on the postfix mailing list
and a couple other sources. Almost all the information below is
applicable no matter which email server you use."