Images in email signatures – linked or embedded?

The HTML format makes it possible to add images to emails and email signatures. Graphics can be included as:

• linked (online) images, which aren’t a part of an email but are fetched from external locations (servers) when a recipient reads the email. Linked images are referenced in the email's HTML source code by using a URL to an external location, e.g.

  <IMG src="https://www.codetwo.com/images/image.jpg">

• embedded images, which are a part of an email body. Only local graphics can be used as embedded images - they are added to emails as hidden attachments and are referenced in the email's source code via a Content-ID:

  <IMG src="cid:unique-content-id">

In the table below you can learn about the advantages and disadvantages of each method.

General tips on using embedded and linked (online) images in email signatures

In general, embedded images should perform better for most common email signature scenarios. They are an integral part of an email, which makes them more reliable – your recipients don’t need to perform any additional actions to see your email signatures exactly the way you designed them (Fig. 1.). That’s why, it’s a good idea to add you company logo, social media icons, or marketing banners as the embedded images. These elements are usually not that big in size (e.g. less than 0.5 MB), so your emails should not increase that much in size.

Fig. 1. Email signature with embedded images (left) and with linked/online images (right) – to see online images, your recipient must click the highlighted message first.

On the other hand, linked/online images are a better solution if you are concerned about the size of your emails. For example, you want to add a high-resolution image to show off your product directly in your email signature, and the image is big in size (e.g. above 1 MB). In such a case, adding an online image that links e.g. to your server/website is a better idea to avoid clogging your and your recipients’ mailboxes with large amounts of data, which is not that difficult even if you don’t exchange a great number of emails.