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What is the best way to design my marketing emails?

Good marketing emails look right in every inbox, are easy to read quickly, and reach the inbox in the first place. Follow these guidelines when building emails in HubSpot or any email platform.

Make sure your emails get delivered

Gmail, Yahoo and Microsoft now reject marketing emails that don't meet their sender requirements. Before sending:

  1. Authenticate your sending domain. Set up SPF, DKIM and DMARC for the domain you send from. In HubSpot, connect and verify your email sending domain; the Gate 39 team can help with the DNS records.
  2. Make unsubscribing easy. Every marketing email needs a visible unsubscribe link. HubSpot adds this automatically; don't remove it from templates.
  3. Keep your list clean. Only email people who opted in, never use purchased lists, and remove contacts who haven't engaged in a long time to keep spam complaints low.

Design

Email clients display emails differently, so keep the design simple and test before sending.

  1. Use your email editor's templates. HubSpot's drag-and-drop editor builds email-safe code for you. If you use custom code, stick to simple table-based layouts.
  2. Use background images carefully. Always set a fallback background color, and never put important text or buttons only inside an image.
  3. Stick with standard fonts if possible. If you use a custom web font, set a standard backup font such as Arial or Georgia.
  4. Check dark mode. Preview how your colors and logo look in dark mode, and use a logo version that works on dark backgrounds.
  5. Design for accessibility. Add alt text to every image, use at least 14px body text, and make sure text contrasts clearly with the background.
  6. Always preview on mobile. Most emails are opened on phones. Send a test to yourself and check it on both a phone and a desktop.

Content

Your email competes with dozens of others in the inbox, so every part should be quick to read and act on.

  1. Write a clear, attention-grabbing subject line, and keep it short enough to show on a phone.
  2. Add preview text. It's the short line that appears after the subject in most inboxes. Use it to add detail rather than repeating the subject.
  3. Keep content short, around 3–5 short paragraphs at most.
  4. Make text scannable with headings, bold text and bullet points.
  5. Stick to one main call to action (CTA) per email, such as "Request a consultation."
  6. Show your CTA as both a button and a text link, so readers can act even if images don't load.
  7. Use personalization tokens, such as First Name, and always set a default value (for example, "Friend") for contacts missing that information.
  8. Offer a web version link for readers whose email client doesn't display the email correctly.

Measure the right results

Some email apps, including Apple Mail, open emails automatically for privacy reasons, which inflates open rates. Use click rate and conversions as your main measures of success, and treat open rates as a rough guide only.

References
[1] MailOver – Google, Yahoo & Microsoft Bulk Sender Requirements: 2026 Guide
[2] EmailWarmup – Gmail and Yahoo Bulk Sender Requirements (Updated for 2026)
[3] Signet – Gmail Yahoo Sender Requirements (With Microsoft 2025)