SPF records are a good way to ensure your email is not marked as spam. To add this to your domain:

1. Login to Manage Domain at http://4domains.com/manage
2. Click either Install or Login under DNS Settings at the bottom
3. At the bottom, enter @ for the first Data text box, then change "IN A" to TXT Record in the middle drop down box, and enter "v=spf1 include:mail.your-domain.com ~all" with the quotes in the last text field
4. Click Add to finish