That's a great question! There are common things that can trigger spam filters, sometimes it can be as simple as the email's content or subject line. For your subject line, it's important to have no more than 4-7 words or 40 characters. As for the contact, you want to stay away from using too many images, or creating an email that is all one image. It's important to have a good balance of text, images and links with targeted content.
If you wanted to take it a step further and try to improve your open rate - creating enticing subject lines, adding personalized contact details or even an emoji are great ways to stand out in your reader's inbox.