How Outlook affects images in email signatures for everyone

Microsoft Outlook is one of the oldest email clients still on the market and still very popular with large corporations. Unfortunately it has some eccentricities that can make it "not play nice" with other email programs like Gmail, Apple Mail, and others. Some of these complexities come from the way that it handles images in an email, or more specifically, in email signatures, which will be our focus today.

When I say Microsoft Outlook here I am referring to the Desktop versions of Outlook, and that includes both Windows and Mac. What I am talking about below is not always true of the Outlook Online web version of Outlook, or the mobile apps for Outlook that are available on iOS and Android.

While Outlook is still popular in corporate environments, its overall market share has decreased over the years. Litmus pegs Outlook's market share in 2022 around 4%, whereas Kinsta says it may be as high as 8%. But it is likely that if you are in a business environment then these statistics would be higher for you and your team.

The Basis: Outlook Embeds Images

When you add an image into your email signature, the desktop version of Microsoft Outlook handles images very differently than other email apps. It embeds the image into the email. This is true whether you choose an image from your computer, or whether you are pasting a signature from a generator like this one. Outlook may embed images because they feel is is a more secure way of sending images, or it may just be the way they started with and they don't want to change it now. I will explain the differences below:

  • Remote Image: The image is actually stored on a server somewhere on the Internet. It has a URL, or an address that represents it such as The email doesn't actually contain the image, but rather just the information of where the image is stored. When you read the sending email, your email program knows to go and get the image from the remote server and display it within the contents of the email.
  • Embedded Image: An embedded image is converted to a CID image, where the contents of the image are converted to a certain type of code and put directly into the contents of the email. So when you send the email, you are sending both the text and the image together and there is nothing to be loaded from a remote server elsewhere on the Internet.

Both of these methods have advantages and disadvantages, which is probably why the standard for emails has never quite solidified in the way that it should have. Generally all email clients have to support both of these methods in some way, but that doesn't mean that you won't notice some of the downsides mentioned below.

Outlook to Outlook - Images Work Perfectly

If you are purely sending emails from Outlook to Outlook, such as within a single company that is all on the same platform, then you probably won't notice any issues at all! Embedded images work well in the Outlook ecosystem. The best thing is that embedded images never require you to choose to display them, so many Outlook users are used to their inter-office emails not requiring them to give permission to display the images within an email.

Other Email App to Outlook - Outlook Hides Remote Images Until User Allows Them

The confusing part happens when those Outlook users get an email from someone who is not using Outlook and the images aren't displayed! For mostly security purposes Outlook will not automatically download these images until the user chooses to download and display them. There is usually a message at the top of the email, as well as showing each of the images with a red X and the text "Right-click or tap and hold here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture from the Internet..." you can see what this looks like in the screenshot below.

Outlook not displaying images

Unfortunately there is no way for the person sending the image to change this behavior. It is up to the receiver, not the sender. That said, there also isn't anything a signature generator like this one can do to change this behavior either. It is a security setting in the reciver's Outlook program and cannot be controlled by the sender of the email. That said, if the receiver adds the sender's email or domain to their "Safe Senders List" then any images received in the future from that sender will be automatically downloaded.

The receiver may be able to turn this setting off (if their company allows them to) by changing their Outlook settings. They can change this setting by following these directions:

  1. Go to File > Options > Trust Center.
  2. Then click "Trust Center Settings".
  3. Clear the "Don't download pictures automatically in HTML e-mail messages or RSS items" check box.

If you are the IT administrator of the Outlook software for your company, there should also be a way to change this setting on a company wide basis.

Outlook to Other Email App and Back - Reply Images Can Get Lost

Email apps generally work well enough together with both remote images and embedded images to display the image. But differences start happening as soon as you hit Reply or Forward. Some email programs will automatically remove any embedded images in the email signature when you reply or forward an email. Some email programs allow you to change this behavior as a setting, but it is often set by default to remove embedded images. This means that the receiver of the reply or forward, will no longer be able to see the image, but often they can still see that an image used to be there. One of the most common places to see this happen is when you send from Outlook, to an iPhone, and reply back to Outlook again. By the time the email makes this round trip the images are often missing.

email signature missing images

There are a number of frustrating things that can happen to an email signature when replying or forwarding the signature. We have a whole article that goes in depth about images and other issues that can happen in a reply/forward. If you want to learn more about that I recommend that as a resource.

Outlook Can Change the Quality of the Images it Embeds

If you are a designer, or have a keen eye for detail, the last thing you might notice is that Outlook can change the quality of the image as it embeds it into the email (and email signature). Since Outlook is trying to make the performance of their email program faster, they compress the image as they embed it to make it as small as possible. This generally is a good thing, but for certain images/graphics can end up being a bad thing.

Compressing an image can result in some details being lost or a slight pixelated pattern being visible within regions of the image. It is especially noticeable when your logo or image has especially fine lines or details in it, or maybe if you use small text or a font with very thin lines. These situations are most frustrating because it can effect the readability of your logo or the information in your graphic.

Outlook embedded image compression

If this bothers you, then if you have Outlook for Microsoft 365 Version 2007 or later, there is an option to prevent the compression of pictures. You can follow these directions if you would like to turn it off. Again, it may also be possible for an Outlook administrator to change this setting for their whole company at a time.

  1. Go to File > Options > Mail.
  2. Then click on "Editor Options".
  3. Then in the left sidebar click "Advanced".
  4. Under the "Image Size and Quality" heading, clear the "Do not compress images in file" check box.

We all wish that things would be easier and more compatible in the email world, and while these discrepancies are frustrating to users, you can understand why Microsoft has made some of these trade offs to make things easier and more secure for their users. We can only hope that large organizations like Microsoft, Apple, and Google will continue to work together to make emails more compatible in years to come and that a agree on stricter standards would help the email industry move forward in the future. But for now, we will just have to use our workarounds that we have available to us and be ok with the rest of it.

Let me know if I didn't mention a frustration you have had with Outlook and images and I will continue to add to it.

Further reading

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