Optimize your email content and design
The content of your emails, both the wording and the design/formatting, can impact whether they get past spam filters and engage readers. Here are best practices to ensure your content doesn’t hurt deliverability:
Write clear, non-spammy subject lines: Your subject line is the first thing both the user and spam filters see. Avoid gimmicky tactics: Don’t use ALL CAPS, avoid excessive punctuation (e.g., “!!!”), and be cautious with words that are common in spam. Words like “Free $$$,” “Act Now,” “Guaranteed Winner,” etc., can trigger filters if used too much. That doesn’t mean you can never say “free”: just use marketing language thoughtfully and sparingly.
Make your subject line relevant to the content and your audience. A good rule of thumb from the experts: If it sounds like something a dodgy used car salesman would say, it’s probably a spam trigger. Instead, focus on clarity and value: “Exclusive 20% off your next order” is better than “!!!EXCLUSIVE FREE OFFER CLICK NOW!!!.” Also, keep it reasonably short and to the point.
Avoid certain flagging elements: There are certain content elements that are no-nos for deliverability:
Large Image-only Emails: Emails that contain a single large image (with little or no text) are often spam. Always cell phone database include appropriate text content, not just images, because filters cannot read images and therefore treat image-only emails with suspicion.
Attaching files (PDFs, Word documents, etc.) to mass emails is generally discouraged. Attachments can contain viruses, so many email systems block them or flag the email. Instead of an attachment, host the file on your website and link to it.
Embedded media or scripts: Don’t try to embed video players, Flash, or complicated JavaScript in an email. Most email clients will strip or break them, and even attempting to include them could trigger filters. A safer approach is to include a thumbnail image with a play button that links to a video on your site, rather than embedding a video. Likewise, use plain HTML and inline CSS; avoid elaborate interactive forms or scripts in emails (they probably won’t work and may look suspicious).
Optimize text-to-image ratio: A common best practice is to have a good balance of text and images. Text-only emails can seem simple (and image-only emails are terrible, as mentioned), so mix them up. Provide meaningful text that describes images (including ALT text on images). Many spam filters want to see at least some text. Also, some users have images turned off by default, so an email should still convey something with images turned off.