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Using hotlinked vs embedded images in Outlook


You wish to evaluate the advantages and disadvantages of using hotlinked vs embedded images in Outlook.


When adding images to an email, it possible to do this using 2 methods; you can either embed the image directly into the email itself, or by using a hotlink to an image hosted on the Signature 365 portal.

By default Signature 365 is configured to embed all images inserted as part of the Signature; this setting is tenant wide and can be changed on request by the support team.

Please note: It is only possible to hotlink to images uploaded to Signature 365. This is to ensure that images are always available to the service

Email clients will in general display images in emails without issue, however there are some cases where either method can cause issues.

This article will cover these differences, and software bugs that can be experienced when using these methods.

Hotlinked images

Hotlinked images are hosted within Signature 365, but are publically accessible. These images are referenced in the HTML source of the signature itself, but are never added to the content of the email.

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  • Image size does not affect the size of the email
  • Images are not removed by the end use email client
  • Images are not affected by the Outlook bug where images are displayed as attachments
  • Image quality does not degrade when replied
  • Images are not seen as attachments by external mail plugins


  • Mail clients may require you to Click here to download pictures before being displayed
  • Requires a connection to the web to view the images

Embedded Images

Embedded images are physically attached to the body of the email when a Signature is inserted. The images are added to the content of the email and do not rely on an external source.


  • Images are always contained within the email
  • Clients are not required to download images
  • Images can be seen by all recipients


  • Increases the amount of data consumed by the email
  • Image quality degrades after multiple replies
  • Images can be seen as attachments by external mail plugins

Which option should your company use?

If you use a specific mail plugin or a customer that has issues with embedded images, you may have little choice but to use hotlinked images.

Generally embedded images are the recommended solution as this ensures that the signature images will be visible to your recipients even if they do not download images as default. It may be worth using hotlinked images if the majority of customers use mobile devices or use webmail clients such as gmail or similar.

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