`Images in this message are hidden. This message might be suspicious or spam.` in gmail when sending transactional email with resend/react email

Question

I'm experiencing an issue with Gmail hiding images in transactional emails sent through Resend, despite having proper DNS configuration and verification.

Setup:

• Turborepo monorepo deployed on Vercel
• Multiple apps in /apps folder, each with its own subdomain (e.g., https://a.example.com, https://b.example.com)
• Using Resend for transactional emails with React Email templates
• All DNS records properly configured (verified green checks in Resend dashboard - Insights tab)
• Domain and email authentication are properly set up

Issue: When Gmail users receive the transactional emails, images are hidden by default with the message:

"Images in this message are hidden. This message might be suspicious or spam."

Important Details:

• Emails are delivered to inbox (not spam)
• Only one image per email (company logo)
• No tracking pixels or suspicious content
• Image is stored in the app's /public folder
• Image URL format: https://b.example.com/logo.png
• Other email clients that I've tested display images correctly
• Resend dashboard shows all green checks for email delivery and authentication
• Only Gmail exhibits this behaviour
• Clicking Show Images does work and render the company logo as expected

Example Email Template:

<Img
  src={`${getBaseUrl()}/logo.png`}
  width="146"
  height="40"
  alt="Company Logo"
  title="Company Logo"
/>

I tried:

1. Following Resend's documentation for proper DNS setup and domain authentication (SPF, DKIM, DMARC)
2. Verifying the image URL matches the sending domain
3. Setting proper image dimensions and alt/title tags
4. Ensuring image is served over HTTPS
5. Checking Resend's dashboard insights which show all green checks for email deliverability

Expected behavior:

• Images should display automatically in Gmail, just like they do in other email clients (Outlook, Apple Mail)
• No "Images are hidden" warning message

Actual behavior:

• Gmail hides images by default with warning: "Images in this message are hidden. This message might be suspicious or spam."
• Users must click "Show images" to see the company logo
• Other email clients display images correctly without any warnings