Embedded vs hosted images in email signatures

Introduction

Many people face difficulties when it comes to adding images to email signatures. Even after mastering basic tasks, more complex challenges like choosing between embedded and hosted images in email signatures can be confusing.

There’s often a lack of understanding about embedded and hosted images. But it’s not as complex as it sounds.

To put it simply, embedded images are those stored within an email. Hosted images are downloaded and stored on a web server. This reduces the size of the email, making it more mobile-friendly. 

If you’re using Microsoft 365, our email signature solution takes the guesswork out — giving you centralized control over how images are managed and displayed across your entire organization's email signatures.

Should we be hosting or embedding images in our email signatures?  

To include HTML images in email signatures like a company logo or social media icons, you’ve got two image options. You can either embed an image directly into the email signature template or host it externally and link to it. 

Deciding whether to host or embed images in your email signatures depends on factors like compatibility, deliverability, branding consistency, and how much control you need over the image once the email is sent. Here's a breakdown to help guide your decision:

Embedding images

This is when the image is encoded directly into the email as a base64 string or attached to the message.

Pros:

• Displays offline: Once downloaded, images remain visible even if the recipient is offline.

• No external calls: Better for privacy-conscious environments or secure email setups.

• Ideal for internal-only email chains: Works well in controlled environments like Microsoft Outlook or within the same organization.

Cons:

• Increases email size: Emails become heavier, which may slow down load times or trigger spam filters.

• Inconsistent rendering: Some email clients (like Gmail and Apple Mail) strip embedded images, leaving only an attachment.

• Difficult to update: Once sent, the image is locked. If branding or banners need to change, you can’t update them retroactively.

Hosting images (web-linked images)

This is where the image is stored on a server and referenced via a URL in the email signature.

Pros:

• Lightweight emails: Keeps the message size minimal, speeding up delivery and avoiding spam flags.

• Brand control: You can update or change hosted images at any time without needing users to change their signature.

• Tracking capabilities: Allows analytics like image loads and click tracking if hosted via signature management platforms like Exclaimer.

Cons:

• Blocked by default: Some email clients block external images by default, requiring recipients to manually enable them.

• Requires connectivity: Images won’t load if the recipient is offline or behind strict firewalls.

• Potential branding issues: If the image host is down or blacklisted, your branding disappears or appears broken.

Which email clients can display embedded images? 

Which email clients can display hosted images?

* To add a linked image, you need to open the image in a browser and copy it into the Microsoft 365 (Office 365) OWA signature editor. 

** You can add a hosted image by adding the HTML source via the signature editor. 

How to embed images in email signatures 

If you want an image to appear without the recipient having to click a ‘Download Images’ button, we recommend embedding it within the email signature.

Here's how to do it:

Step 1: Add the image to your email signature

Most email clients allow you to add an image to your signature. Insert the image as you normally would, making sure it’s properly sized.

Step 2: Set up the Content-ID reference

When embedding, the image is attached to the email and referenced with a Content-ID. This is done by adding HTML code in the signature's source.

A standard Content-ID will look like this: 

<img src="cid:myimagecid" /> 

Step 3: Save and test

Once you’ve added the Content-ID reference, save your signature and send a test email to yourself. If set up correctly, the image should display automatically without needing to download it. This is because they’re referenced in the source of the message. 

Important considerations

• Embedded images may increase email size, which can cause them to appear as attachments in some clients.

• There are also known issues with images being stripped out of emails and increasing in size on iOS devices. 

How to host images in email signatures 

To prevent images in your email signature from appearing as attachments, you can host them on a web server or a free image hosting site like Imgur or Flickr. This method references the image using a web URL, so the image remains separate from the email itself.

Here’s how to do it:

Step 1: Upload your image

Upload your image to a web server or an image hosting platform. Once uploaded, the platform will provide you with a direct URL to the image file.

Step 2: Link the image in your email signature

Use HTML to reference the hosted image URL in your email signature. A typical example might look like this:

<img src="https://cdn.exclaimer.com/Static2/exclaimer-logo_178x36.png" />

This code links the image to your email signature without attaching it, keeping your email file size smaller.

Step 3: Add alt text (optional but recommended)

Adding alt text (alternative text) ensures that recipients can understand the purpose of the image even if it doesn’t load. You can add alt text by including an alt attribute, like this:

<img src="https://cdn.exclaimer.com/Static2/exclaimer-logo_178x36.png" alt="Exclaimer logo"/>

Important considerations

• Download prompt: Hosted images may prompt recipients to click ‘Download Images’ to view them, a security feature designed to protect against potential risks.

By hosting images this way, you ensure that they aren’t embedded in the email, keeping the email lighter and often improving compatibility across devices and email clients.

Which option should I choose to show images in email signatures? 

You need to consider how your customers/clients view the emails you send them.

If many use email clients like Outlook365, embedding images in email signatures is recommended.

However, you should use hosted imagery if you know that many recipients will be viewing your emails on mobile devices.