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Explanation

Email Flow Image Rendering

Last Updated: June 25, 2026

Table of Contents​

Overview​

When a merchant uploads an image to an email flow in UltraCart, the image undergoes background processing before it is fully available for delivery. Test emails sent immediately after upload may render the image incorrectly or not at all on certain email clients, particularly iPhone Mail. The issue resolves on its own once processing is complete.

This document covers expected image processing behavior and how to diagnose rendering issues that appear only on mobile devices.

How Image Processing Works​

After an image is uploaded to an email flow, UltraCart performs background optimization and makes the image available via CDN. This process typically completes within one to two minutes. During this window:

  • The image URL is already embedded in the email template

  • A test email sent before processing completes will include the URL, but the image may not yet be fully available at that URL

  • Some email clients, particularly iPhone Mail, will fail silently or display a broken image when the asset is not yet available at delivery time

  • Desktop clients and some Android clients may render the image correctly because they are more tolerant of slow or delayed asset availability, or they re-fetch the image when the email is opened

Once processing completes and the CDN propagates the asset, subsequent test sends and all live sends will render correctly.

Troubleshooting​

Image renders broken or missing on iPhone but fine on desktop​

Symptoms: Merchant sends a test email immediately after uploading a new image. The image appears broken or missing when the email is opened on an iPhone. The same email renders correctly on a desktop browser or Android device.

Root Cause: The image was not yet fully processed or propagated to CDN at the time the test email was delivered. iPhone Mail fetches images at delivery time with limited retry behavior; if the asset is unavailable at that moment, it renders as broken and does not retry.

Diagnosis: Ask the merchant:

  1. How soon after uploading did they send the test email? (Less than two minutes suggests a processing delay.)

  2. Did the issue resolve on a subsequent test send without any changes? (Self-resolution confirms processing delay rather than a configuration problem.)

  3. Is the rendering issue limited to the first test send, or does it persist?

If the issue self-resolved without the merchant changing the image or template, background processing delay is the most likely explanation.

Solution:

  1. Wait one to two minutes after uploading a new image before sending a test email.

  2. If the rendering issue has already appeared on a test send, send a new test email without making any changes — the image should now render correctly.

  3. If the issue persists beyond two minutes on repeated test sends, the image itself may be the problem.

Image renders broken on repeated test sends​

Symptoms: The image renders incorrectly on multiple test sends across different clients, and the issue does not self-resolve.

Root Cause: The uploaded image may have a format or encoding issue that causes processing to fail, or the image block configuration in the email template may be incorrect.

Diagnosis:

  1. Check the image file format — UltraCart accepts JPEG, PNG, GIF, and WebP. SVG and HEIC files may not process correctly.

  2. Verify the image is not corrupted and opens correctly in a standard image viewer.

  3. Re-upload the image and wait two minutes before sending a new test.

Solution:

  1. Re-upload the image in a supported format (JPEG or PNG recommended).

  2. If re-upload does not resolve the issue, contact UltraCart Support with the flow name, email name, and a screenshot of the rendering issue.

Best Practices​

  • Wait at least one to two minutes after uploading any new image before sending a test email. This ensures the image has fully processed and is available on the CDN.

  • If a test email shows a broken image, send a second test before making any changes. Processing delay is the most common cause and requires no action.

  • Use JPEG or PNG formats for email images. Keep file sizes under 1 MB where possible to reduce processing time and improve email client load performance.

  • Test emails on both desktop and at least one mobile client (iPhone Mail and Gmail on Android cover most merchant customer bases).

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