4 Best Practices to Keep Marketing Emails Out of Spam Filters

Spam: It’s exactly where you don’t want your marketing emails to go. But each year, 18% of emails in the U.S. wind up there, according to Return Path.

That’s bad news if 1 in 6 recipients never sees your message — especially when they signed up to hear from you.

Fortunately, avoiding spam filters is doable with the right approach. At Zoe Marketing & Communications, we’ve managed thousands of email campaigns since 2020, crafting emails that reach inboxes and get results.

Here’s how to keep your emails clean and delivering successfully.

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5 best ways to keep your marketing emails out of spam filters

1. Craft subject lines that avoid spam filters

Your subject line determines whether people open your email — or if it lands in spam. Both email platforms and recipients flag suspicious emails based on subject lines alone.

Avoid gimmicks

• No ALL CAPS
• No excessive punctuation!!!
• No awkward capitalization tricks (LiKe ThIs)

Skip salesy language

• Words like “free,” “buy now” or “earn cash” are classic spam triggers.

Stick to best practices

• Keep it under 60 characters (so it’s fully visible on mobile).
• Check spelling and grammar (mistakes look like scams).
• Personalize when possible (a first name can boost opens by 26%).
• Use emojis sparingly (one is fine — too many look unprofessional).

2. Use images correctly

Images grab attention inside an email, but using them incorrectly can send your email straight to spam.

Common mistakes

• Sending an image-only email. Spam filters can’t read text inside an image, so emails with no typed content look suspicious.
• Too many images. This throws off the text-to-image ratio and slows load time.
• Large file sizes. High-resolution images can cause clipping (where part of your email gets cut off).

Best practices

✔ Include both text and images. Balance your content.

✔ Keep images under 200KB and in JPG or PNG format (72 DPI for web).

✔ Never attach files. Instead, upload PDFs or videos to your website and link to them.

✔ Use GIFs sparingly. They add motion without bloating file size.

3. Keep body copy clean

After your subject line, spam filters scan your message body for red flags.

Avoid

• Over-the-top sales language (e.g., “ACT NOW!”).
• Excess formatting (too much bold, italics or large fonts).
• Keyword stuffing (repeating the same terms unnaturally).
• Writing too much. Long emails risk being clipped, which hurts engagement.

Do

✔ Write naturally. Keep it simple, direct and conversational.

✔ Use consistent fonts. Stick to one or two easy-to-read styles.

✔ Have a clear CTA (call to action). Tell people exactly what to do next.

✔ Keep it short. For single-focus emails, 25-100 words is enough. Newsletters should be concise and scannable.

4. Follow general email best practices

A few technical missteps can still send a solid email into spam.

✔ Always include an unsubscribe link. It’s required by law and protects your sender reputation.

✔ Never embed a form. Forms don’t work inside emails. Link to them instead.

✔ Don’t buy email lists. They’re full of bad addresses and increase your spam risk.

✔ Scrub your email list. Remove inactive addresses regularly to maintain deliverability.

✔ Test before sending. Preview your email on Gmail, Outlook and mobile to spot formatting issues.

Next steps for email marketing success

Landing in spam wastes time and money. But with clean subject lines, optimized images, balanced copy and smart email practices, you can keep your emails inbox-ready.

Need help getting started? Talk to us here at Zoe Marketing & Communications for expert email marketing strategies.

Still learning about email marketing? Learn more about:

• The key benefits of email marketing
• How targeted email marketing works