In nonprofit email marketing, there’s not much worse than creating a great campaign, building a compelling message, and then ending up in someone’s spam folder.

So how do you avoid that? You need to know what triggers spam filters. Here are three ways to get your messages delivered to someone’s inbox and stay out of their junk folder.

Don’t send attachments.

If you include attachments with your messages, they’ll automatically be marked as spam because many attachments include viruses. Avoid sending attachments at all costs.

Watch your graphics.

A large use of graphics is a big red flag for email clients. Graphics should compliment text, not vice versa. To be safe, stick with the 80/20 rule—80% of the message should be comprised of content and text and 20% in supporting graphics. Follow this rule and the algorithm used by most email service providers will identify your message as a potentially viable email. More graphics than text? It’ll be identified as potential spam.

Watch your words.

Some are associated with spam and they may land you in someone’s junk mail, particularly if used in the subject line. Risky words include free, prize, bonus, buy, purchase, promotion and deal. Also, watch your punctuations—exclamation marks are especially risky in subject lines, as are words in ALL CAPS.

When you build your next email campaign, focus on delivering the right message to your audience, but be mindful of what sends the wrong message to spam filters. A great campaign that gets labeled as junk mail will be sadly ineffective.