Well-designed emails help improve deliverability. They also reduce the chances of subscribers marking messages as spam. Follow these design best practices to help your campaigns reach more inboxes.
Write Strong Subject Lines
Subject lines play a major role in whether your email reaches the inbox. Spam filters often analyze subject lines first.
Avoid All Capital Letters
Avoid writing subject lines in ALL CAPS.
All caps can look aggressive or spam-like. Spam filters may flag the email.
Use Curiosity or Questions
Write subject lines that spark curiosity.
Questions often increase open rates.
Examples:
“Did you get what you were looking for?”
“Hi [Name], quick question?”
“You are not alone.”
Limit Exclamation Marks
Avoid using multiple exclamation marks.
Use a question mark instead when possible.
Avoid Spam Trigger Words
Some words commonly appear in spam emails. Avoid using them.
Examples:
Free
Best price
Cash
No obligation
Optimize the Email Body
Spam filters also scan the content and structure of your email. Your design choices can affect deliverability.
Avoid Attachments
Do not attach files such as:
Word documents
PDFs
Attachments often trigger spam filters.
Instead:
Upload the file to a website.
Add a link or call-to-action (CTA) to download it.
Use Simple Fonts and Styles
Use standard fonts and consistent styling.
Best practices:
Use one or two fonts only.
Keep font sizes consistent.
Limit the number of colors.
Use Relevant Images
Images should support the message.
Too many images can:
Increase load time.
Reduce deliverability.
Add Alternate Text to Images
Some email clients block images.
Add alternative text (alt text) for every image.
Alt text describes the image when it does not load.
Check Spelling and Grammar
Spelling errors can harm credibility.
Poor grammar may trigger spam filters.
Always proofread before sending.
Include an Unsubscribe Link
Every email should include an unsubscribe option.
Benefits:
Protects sender reputation.
Builds trust with subscribers.
Helps comply with email regulations.
Tip: Create a Merge Tag as a Special Link. This makes it easy to insert the unsubscribe link into your email footer.
Maintain a Healthy Image-to-Text Ratio
Emails should contain mostly text.
Recommended guideline:
Images: 30–40% of the email
Text: 60–70% of the email
Spam filters often flag emails that contain too many images.
Avoid URL Masking
Do not hide or shorten URLs.
Masked links can look suspicious to spam filters.
Always use clear and transparent links.
Monitor Email Deliverability Factors
Several technical factors also affect inbox placement.
Email Authentication
Set up proper authentication for your sending domain.
Common authentication methods:
Authentication | Purpose |
SPF (Sender Policy Framework) | Confirms approved sending servers |
DKIM (DomainKeys Identified Mail) | Verifies message integrity |
DMARC (Domain-based Message Authentication, Reporting and Conformance) | Adds policy and reporting for authentication |
Bounce Rate
A bounce occurs when an email cannot be delivered.
High bounce rates may damage sender reputation.
Reduce bounces by:
Removing invalid addresses
Keeping lists updated
Blacklists
Sending domains or IP addresses can appear on spam blacklists.
Monitor your sender reputation regularly.
Take action if your domain appears on a blacklist.
Maintain List Health
Use a clean and engaged subscriber list.
Best practices:
Remove inactive contacts
Remove invalid addresses
Use double opt-in when possible
Protect Your IP Reputation
Send emails gradually when starting a new domain or IP.
This process is called IP warming.
Gradual sending builds trust with mailbox providers.
Pro Tip: Test Emails Before Sending
Test your email before launching a campaign.
Spam testing tools identify potential issues early.
Recommended tool:
Testing helps detect:
Spam trigger words
Authentication issues
Design problems
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