Email providers like Gmail, Yahoo, and Outlook use spam filters to evaluate campaign content. Even legitimate senders can be filtered if campaigns include spam triggers (all caps, misleading subject lines, image-only emails).
This article shows you how to optimize Email Campaigns for inbox placement.
Before You Begin
Before optimizing campaign content, verify:
Domain authentication: Set up SPF, DKIM, and DMARC.
Engagement segmentation: Send only to Contacts who opened or clicked in the last 6–12 months. Improve Deliverability with Engaged Contacts.
Test campaigns: Send campaigns to your test email addresses in Gmail, Yahoo, and Outlook to check spam folder placement.
💬 Learn more: Get Started with Email Deliverability in Omnisend.
Be Consistent with Your Sender Identity
Spam filters analyze sender name consistency. Switching between personal names and company names confuses recipients and providers.
Best practices:
Use your company or brand name (e.g., "Omnisend") unless the person is the brand (e.g., "Jamie Oliver").
If using a personal name, include your company: "Jane – Omnisend Team."
Never switch sender names between campaigns.
⚠️ Avoid special characters and emojis in sender names.
Gmail and other providers may filter campaigns with special characters (e.g., ™, ®, ★) or emojis in the sender name. This can cause delivery failures for contacts. Use plain text only: "Omnisend" instead of "Omnisend ✨" or "Omnisend™".
Write Clear Subject Lines & Preheaders
Subject lines and preheaders are the first elements recipients see. Misleading or spammy subject lines generate unsubscribes and spam complaints.
Subject Line Best Practices
Avoid:
❌ All caps: "FREE PRIZE!!!"
❌ Excessive punctuation: "Click here now!!!!"
❌ Misleading claims: "You've won $1,000!" (when they haven't)
❌ Hash-busting: "F.ree p.r!z.e"
Use:
✅ Clear, honest phrasing: "Your exclusive discount is ready (15% off)"
✅ Task-oriented language: "Complete your order and save 10%"
✅ Brand name: "Omnisend – Your campaign report is ready"
Length: Keep subject lines under 70 characters to avoid truncation on mobile.
💬 Read more:
Preheader Best Practices
The preheader appears after the subject line in inboxes. Use it to expand on the subject line, not repeat it.
Example:
Subject: "Your exclusive discount is ready"
Preheader: "Save 15% on your next order – expires Friday"
💬 Read more: The Secret Power of Email Preheader: DOs and DON'Ts.
Optimize Campaign Content
Spam filters analyze campaign structure, image-to-text ratio, and wording.
Maintain a Healthy Text-to-Image Ratio
Avoid image-only campaigns. Spam filters flag campaigns with little or no text.
Best practice: Use a 60:40 text-to-image ratio (60% text, 40% images). For every image, include 2–4 sentences of text.
Avoid Spam Trigger Words & Phrases
Certain words and formatting patterns trigger spam filters. Avoid:
❌ Excessive exclamation points (!!!!!!).
❌ All caps in subject lines or body text.
❌ Aggressive sales language: "Click here!" "Once in a lifetime opportunity!".
❌ Overuse of: "free," "prize," "bonus," "guaranteed".
❌ Inserting random characters in the subject line (e.g., "F.ree. p.r! z.e").
❌ Sending a test to multiple recipients within the same company (e.g., your colleagues). The company's email firewall may assume it's a spam attack.
💡 Use promotional language moderately. You can still use "free" or "bonus" – just avoid clustering multiple trigger words in one sentence.
Make the Unsubscribe Link Easy to Find
Legal requirement (CAN-SPAM Act): Every Email Campaign must include an unsubscribe link.
Place the unsubscribe link in the footer where recipients expect it. If recipients can't find it, they'll mark your campaign as spam instead, which damages sender reputation far more than an unsubscribe.
After recipients unsubscribe, confirm the action: "You've been unsubscribed. You won't receive future campaigns from us." Learn how to manage your Unsubscribe Page.
Optimize for Mobile
Over 50% of Email Campaigns are opened on mobile devices. Your campaigns need to be adapted for both mobile and desktop devices.
Avoid:
❌ Font size below 12pt (hard to read on small screens).
❌ Links too close together (hard to tap without zooming).
❌ Campaigns over 100KB (Gmail clips emails larger than 100KB).
Use:
✅ Minimum 12pt font size.
✅ Buttons instead of text links (easier to tap).
✅ Simple layouts (single-column designs work best).
💡 Tip: Send a test campaign to yourself on mobile before sending to your full list. Check font size, button tap targets, and image load time.
Avoid URL Shorteners
Spammers and phishers use URL shorteners (bit.ly, tinyurl.com) to hide malicious links. Spam filters flag shortened URLs accordingly.
Best practice: Use full URLs from your authenticated domain (e.g., https://yourbrand.com/sale).
Keep Total Campaign Size Under 100KB
Gmail clips campaigns larger than 100KB. When this happens, recipients must click "View entire message" to see the full content.
Problem: If the unsubscribe link is below the clipped section, recipients may click "Report Spam" instead, which damages the sender's reputation.
Campaign size includes:
Text
Images
Links
Tracking codes
Responsive design elements
💡 Best practice: Keep total campaign size under 100KB. Use compressed images and concise copy.
Troubleshooting Spam Placement
If campaigns are landing in spam despite following best practices:
Verify spam placement first: Send test campaigns to Gmail, Yahoo, and Outlook. Check inbox, promotions, and spam folders.
Review engagement metrics: Low open rates, high spam complaint rates, and high bounce rates signal deliverability issues.
Send only to engaged Contacts: Segment by Contacts who opened or clicked in the last 30 days. Gradually increase send volume by 25–35% per campaign.
💬 Recovery takes 2–4 weeks. Learn more: Prevent Campaigns from Landing in Spam.
If issues persist after 2–4 weeks, contact our Support Team at [email protected] or via in-app chat. Our Deliverability team will check and recommend advanced troubleshooting.
FAQ
What text-to-image ratio prevents spam?
Use a 60:40 text-to-image ratio (60% text, 40% images). For every image, include 2–4 sentences of text.
Can I use promotional words like "free" or "bonus"?
Yes, but use them moderately. Clustering multiple trigger words in one sentence (e.g., "Free bonus prize guaranteed!") increases spam risk.
Why are my campaigns clipped in Gmail?
Gmail clips campaigns larger than 100KB. Keep total campaign size under 100KB by compressing images and using concise copy.
Should I include an unsubscribe link in every campaign?
Yes. It's required by law (CAN-SPAM Act). Place the unsubscribe link in the footer. If recipients can't find it, they'll mark your campaign as spam instead.
If you have any further questions, please contact us via in-app chat or at [email protected].