Im not emailing spam ofcourse, just monthly emails to my clients who have agreed to recieving emails from me, however, emails that i sent out, automatically end up in their junk mail, so many of my clients dont get to see it.
Make sure you're not sending email from a 'free' email provider like Hotmail or Yahoo! as these can be automatically marked as Spam.
Register your own domain name, and set up proper mailing list software on it, like PHPList.