Came across an interesting blog post on the topic of how to prevent genuine emails from being flagged as spam.
It goes into some of the technical approaches that can be used to this end.
Another small technique I've discovered (which may be of help to technical and non-technical users alike) is to ensure that you use a more meaningful subject for your email. Also use less commonly used words, or use 1 to 3 extra words (that are still pertinent to the topic of your email) as part of the subject. This is empirical, but I think doing this (using a few extra words or more meaningful / less common words in the subject) helps spam filters to distinguish genuine email from spam.
A side benefit of using this technique:
If you have an email thread going, with multiple emails to and from someone, and the topic of the email changes over time, change the subject of the email to match (and also apply the technique above), instead of just hitting Reply, which would result in the same old subject (which is no longer relevant). This makes it easier to search your mails for the changed topic. In Gmail, you can do this by clicking "Edit Subject" after clicking "Reply".
Vasudev Ram - Dancing Bison Enterprises