Email No Longer Dependable

Thanks to the war between spam and anti-spam, email is no longer a reliable way for communication. Your email could be bounced back because the recipient's email system rejected it, or even worse, the email could be dropped silently without anyone knows its existence.

People hate spam, and so, just like spam, anti-spam is becoming a booming business. There is no need to tell you how bad spam is, because you know it. We here instead intend to warn you that, email filtering of some anti-spam program can do more harm than good.
(More) http://www.websina.com/en/spam.html