Security Policy Errors

Fix Defender Attack Simulation Logo Not Appearing in Emails

Phi Hung Vo Oct 7, 2026 870 views

Question details

The company logo fails to render in delivered Microsoft Defender Attack Simulation Training emails despite showing correctly in the payload preview.

Product: Microsoft Defender
Device & OS: not provided
Scenario: Running an internal email security and phishing simulation using Microsoft template payloads.
Observed behavior: The company logo is fully visible during the Attack Simulation Training preview but disappears completely when the actual simulation email is delivered to users' inboxes.

Before you start

Verify that you have the necessary Security Administrator permissions in the Microsoft 365 Defender portal and use a free online tool to convert your company logo (PNG or JPG) into a base64-encoded string before editing the payload.

Solution 1Recommended

Create a Custom Payload with a Base64-Encoded Logo

Building a custom payload from scratch and embedding the logo directly into the HTML as a base64-encoded image prevents the template from stripping the graphic upon delivery.

Editing existing Microsoft payload templates often results in missing graphics because the simulation delivery mechanism can strip standard image attachments or external URL links. Creating a custom HTML payload with a base64-embedded image ensures the logo data is contained entirely within the email code itself.

Navigate to the Content Library

Log into the Microsoft 365 Defender portal. In the left navigation menu, go to Email & collaboration, select Attack simulation training, click on the Content library tab, and choose Payloads.

Create a New Payload from Scratch

Click the option to create a custom payload rather than modifying a pre-existing Microsoft template. Fill in the required payload details such as name, theme, and language.

Embed the Base64 Image in HTML

In the payload editor, switch to the HTML view. Insert your company logo using an image tag formatted with your base64 string (for example: <img src="data:image/png;base64,YOUR_BASE_64_STRING_HERE">). Make sure to properly set the width and height attributes.

Preview and Send a Test Email

Use the preview function to check the image format and HTML rendering. Send a test email to your own inbox to verify the logo appears correctly in the delivered simulation before launching the campaign.

Proper Image Sizing: Resize your company logo to the exact dimensions you want it to appear in the email before converting it to base64. This minimizes the payload's HTML file size and ensures crisp rendering.

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Frequently Asked Questions

Why does the company logo work in the Defender preview but not in the delivered email?

The preview tool renders HTML directly in your browser, which allows standard image links to load. However, the actual delivery mechanism for default Microsoft templates often strips standard attachments or blocks external image URLs to simulate realistic phishing behaviors. Base64 encoding bypasses this by embedding the image data directly in the HTML.

How do I convert my company logo into a base64-encoded string?

You can use any free online base64 image encoder. Simply upload your PNG or JPG file, and the tool will generate a long text string starting with 'data:image/png;base64,'. You copy this entire string and paste it into the 'src' attribute of your HTML image tag.

Can I edit the existing Microsoft payload template to fix this missing logo issue?

It is generally not recommended. Users frequently report that editing default Microsoft templates still results in missing logos upon delivery due to backend template restrictions. Creating a payload entirely from scratch in the Content Library yields much higher success rates.

Does the image file format affect the simulation email delivery?

Yes. Complex or unsupported formats can break the HTML rendering. It is highly recommended to use a standard PNG or JPG file, resize it appropriately to keep the data string manageable, and then encode it to base64 for embedding.

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