1. Keep your subject line short, simple, and transparent. Don't use caps, or words like "free," "as seen on," "buy," "clearance," "cheap," or any other spammy words. Don't use all caps, either. Keep your subject line short, to the point, and relevant.
2. Make sure the plain text and links are all related to the subject line, and that you write clearly and concisely. Additionally, avoid hard-to-read color schemes: this comes across as spam, and besides, you want your audience to be able to read your email.
3. As with your headline, avoid spam-like copy. Examples include “free,” “bonus” and “no investment.” These can appear in legitimate emails as well, but it’s best to use them sparingly or eliminate them all together.
4. Unsubscribe or opt-out options should be easy to find in your email. Additionally, best practices dictate that you include your address as well. These things are most often found in the footer of the email-- just make sure they're included.
5. Always send your emails from a reputable URL with a brand or person’s name attached.