Here's something I just realized when poking around on one of my servers. Obviously most people in most email lists will be at major email hosts such as gmail, yahoo, etc. but many people have their email hosted on a company or private Linux server. This is even more relevant for lists of business contacts as many such lists I've seen contain a majority of emails hosted in the aforementioned manner. Following this logic we can draw some conclusions about a percentage of the recipients. One conclusion we can draw is that Linux (In particular CentOS) is the most popular OS for hosting an email server. From there we can surmise that the most popular spam filter is SpamAssassin, especially since it's what's used by WHM/CPanel (The most popular panel) and probably other panels as well. So, SpamAssassin is widely used and has many features that people expect will stop spam from entering their inboxes. From Wikipedia "SpamAssassin was awarded the Linux New Media Award 2006 as the "Best Linux-based Anti-spam Solution." So here's the tip. SpamAssassin, with all Its features has one simple out of the box weakness. There's a default option in SpamAssassin that basically ignores any email message above a certain size. When I say ignore I mean that it actually let's the email bypass all filters. The default size threshold is 200KB. All you have to do is make sure that the size of your email is greater than 200KB and your emails will slip right through the filters. Of course if someone has increased this value it won't make a difference but this isn't an option that is presented to the user when setting up the email server. In fact, I've been using SpamAssassin for many years and just now noticed it so it's very likely to be set to 200. Now go on and get those messages into where they belong, Happy Mailing!