Salesforce Marketing Cloud Email Image Sizes and Best Practices

How Content Builder handles email images and campaign assets

Salesforce describes Content Builder as a cross-channel repository for marketing content, including images, email assets, blocks and templates. An image uploaded to Content Builder is therefore part of a wider production workflow rather than a guarantee that it will fit every possible campaign.

Image size depends on where the asset appears: a full-width hero, a reusable header, a two-column promotional tile or a dynamic product recommendation can all require different dimensions. Establish approved display sizes before teams start uploading artwork.

• Separate source photography from campaign-ready delivery assets.
• Name files consistently so marketers can recognise the intended placement and dimensions.
• Keep logos, hero banners and product tiles in organised Content Builder folders.
• Retain a clear distinction between a stored image asset and an editable Image Block.
• Check whether a reusable component is shared across multiple campaigns or business units.

Calculate the correct Content Builder image dimensions

Salesforce Marketing Cloud supports different email templates and custom HTML structures. A 600px content area is a common email-design convention, but it is not an official platform-wide requirement. Some organisations use 640px, another custom width or narrower padded content blocks.

Measure the available inner width after padding, table-cell spacing and column gutters. Treat these dimensions as examples, not a mandatory Salesforce standard.

Set standards for reusable headers, banners and image blocks

Reusable Content Builder blocks can save production time, but a poorly sized image can also repeat the same visual problem across many sends. Define the visible width, preferred aspect ratio, acceptable format and accessibility expectations for each approved component.

Version approved assets carefully. Replacing an image used by multiple campaigns can affect future messages, automated journeys and content that other teams assume is stable.

Use Retina image sources with explicit email HTML widths

A Retina-ready source should improve image sharpness without expanding the visible email layout. When a hero is designed to display at 600px, a 1200px source can provide 2x horizontal detail while the HTML still specifies the intended 600px width.

<img src="https://example.com/campaign-hero-1200.jpg"
     width="600"
     alt="Explore the new seasonal collection"
     style="display:block;width:100%;max-width:600px;height:auto;border:0;">

Check custom HTML blocks, reusable content and any AMPscript-generated markup. A high-resolution source with no reliable display width can render too large in some email clients.

See our Retina Email Images Guide for display-width calculations.

Check desktop and mobile behaviour before approving assets

A responsive Marketing Cloud template may stack columns, change padding or scale a wide banner to a narrow phone screen. These changes affect composition even when the underlying image file technically fits.

• Check that a two-column product row remains balanced when stacked.
• Keep small promotional lettering readable when a desktop banner shrinks.
• Make linked images easy to identify and ensure surrounding calls to action remain visible.
• Test personalised images with short and long customer data values.
• Review both light and dark email-client appearances where practical.

Use a dedicated mobile crop only when the template supports the required behaviour. Do not assume that every Content Builder block automatically provides separate mobile image files.

Account for Outlook rendering and accessible image alternatives

Outlook desktop, Outlook on the web and mobile Outlook applications do not all render email HTML identically. Explicit image widths, dependable table structures and well-defined fallback colours help avoid layout surprises.

Alternative text should describe the purpose of an informative image. If an image is blocked, recipients still need enough context to understand the relevant promotion or action. Avoid putting the only important price, deadline or call to action inside a picture.

Review personalised images, AMPscript and fallback assets

Dynamic campaigns can select different artwork according to subscriber attributes, audience segments or journey conditions. The images should share compatible dimensions and an agreed visual structure so a different record does not break the same email layout.

Salesforce documents ContentImageByKey() as a function that returns an image tag for an Image-type asset in Content Builder. Its documentation specifically states that the function does not work with Image Block content. Confirm the asset type before relying on a dynamic reference.

• Use stable asset references and a suitable default image.
• Check that every personalised variant has a compatible aspect ratio.
• Verify alt text when the visual message changes between segments.
• Preview multiple representative subscribers, including records with missing data.
• Test triggered and Journey Builder messages as carefully as scheduled campaigns.

Teams operating more than one enterprise platform can compare this approach with our Oracle Eloqua email image sizes guide.

Salesforce Marketing Cloud campaign image QA checklist

1. Confirm the template width and the usable width of every image block.
2. Check image pixel dimensions, aspect ratio, format and reasonable file weight.
3. Review alt text, fallback colours and readability with blocked images.
4. Inspect desktop, mobile and high-density display behaviour.
5. Preview representative subscriber records and dynamic content variations.
6. Test linked destinations, campaign tracking and personalised offer consistency.
7. Send live test messages to relevant Outlook, Gmail and Apple Mail accounts.
8. Recheck shared assets before approving a scheduled campaign or automated journey.

For broader planning across email clients, use the Email Image Size Guide.

Frequently asked questions about Salesforce Marketing Cloud images

Official Salesforce documentation and training

• Salesforce Content Builder asset and content documentation
• Salesforce Content Builder content blocks and custom block widgets
• Salesforce AMPscript ContentImageByKey reference
• Salesforce Trailhead email preview, testing and sending guidance

ImageOptimise is independent and is not affiliated with, integrated with or endorsed by Salesforce.