Common image-related problems in signatures


You experience various problems with images in emails, e.g. embedded pictures are not displayed in received emails or disappear when replying/forwarding.


Problems with embedded images may have several causes, with the most common listed below. Usually, if images are suddenly gone from a conversation thread it means the email was either converted to a different format or processed in a way that removed images.

Email client security restrictions or bandwidth usage protection

The information gathered while opening remote resources, including websites, may be used by their owners to identify visitors. As a result, most email clients contain a feature that prevents automatic download of images from external servers. In such a case, instead of the image itself, the email client user might see a small box with a red cross (No picture box) (Fig. 1.), an empty picture frame, or the message might not display any embedded content at all.

Fig. 1. External content blocked by Outlook.

To solve this issue, you can enable downloading remote content from the Internet. You may find such an option directly in the opened message or in the options of your email client. However, if you have enabled this option and still experience the problem, please review your network configuration, especially bandwidth usage protection and also configuration of your security solutions, including antivirus software and SPAM filters.


Please note that owners of the remote servers with images are only able to obtain your IP address and information on the mail client you used to download the images. There is no option to gather any credentials used for authentication on the mail servers.

Email client's default message composing format and conversion

Every mail client can use a different default message composing format. Depending on the platform, you can send your message in HTML, RTF or Plain Text. Usually, when you add any formatting or images to a message, your mail client automatically switches to the HTML or RTF format. Of course, most email clients (including Microsoft Outlook, Thunderbird and Apple Mail) have an option to manually choose which format should be used.


If you use Apple devices, we recommend that you check our Knowledge Base article: Message sent from an Apple device is in plain text.

Currently, we only support HTML signatures with images. Some of the devices (like iPhones and iPads) are, by default, sending messages in Plain Text, therefore you might need to convert them into the HTML format. You can find more information about conversion in the sections below.


Please keep in mind that the OWA app for iOS and Android supports only signatures in Plain Text.

MS Exchange Server format conversion or enforcement

The default settings in Microsoft Exchange Server allow mail clients to send messages in both the HTML and Plain Text formats. Still, emails might be delivered in a different format than original because, for example, third-party MS Exchange Transport agents or antivirus software is set to convert them. MS Exchange Server settings in your environment might also force email format conversion to Plain Text - in such a case, CodeTwo software will add the Plain Text version of a signature, with no images (other images included in a message will also disappear). See this Knowledge Base article to learn how to check and modify your default Exchange Server settings to avoid unwanted conversion from HTML to Plain Text.


If you need to force email format conversion to HTML, you can use CodeTwo software. See this section to learn more.

What is more, Exchange Server and email clients are using specific Content-Transfer-Encoding setting to process the messages. Some of the clients may encounter issues when downloading images and merging them directly with a message. For example, in Thunderbird you may experience a situation when images are located on the list of attachments, instead of within the body of an email. If you have similar problems, we advise you to look for another email application.

CodeTwo and other third-party software message format conversion

Only the HTML format is supported by CodeTwo software when it comes to stamping emails with signatures containing images. That is why sometimes you might need to convert the message body to HTML. Fortunately, some of the CodeTwo products can automatically do that:

Some third-party applications may cause unwanted conversion to the Plain Text format. We strongly recommend to verify your current third-party Exchange tools, add-ins for mail clients and configuration of your security solutions (including SPAM filters and antivirus software).

Native Mail app settings in Apple devices

Prior to the OS X Yosemite and iOS 8, the default behavior of Apple's Mail client was to embed all images found in a conversation. Unfortunately, this was changed at some point and nowadays all images are converted into labels in order to save space in your email. When it comes to iOS devices such as iPhones and iPads, the mail client's default behavior is to remove embedded images.

To restore image embedding in OS X Yosemite, follow these steps:

  1. Open the Mail app.
  2. Open the composing window by opening the message with which you have experienced problems and clicking the reply or forward button.
  3. In the upper-right part of the window, click the button with a rectangle and a paperclip, highlighted in Fig. 2.
  4. All images should become visible.

Fig. 2. How to enable embedding images in messages when replying/forwarding.

To restore images that were deleted by iOS devices, you can use a dedicated action: Restore images removed by iPhone and iPad. The action is available in CodeTwo Exchange Rules and CodeTwo Exchange Rules Pro.

See this article to learn more and see other problems related to mobile devices

The Tap to download button not working in iOS 7 and later

We have also found another problem that occurs in iOS 7 and later. Sometimes, the default mail application displays certain embedded images incorrectly - images are not downloaded to emails, but instead you see the Tap to download button. When you click it, nothing happens. The problem appears only in the case of messages that were replied to or forwarded via the default mail app. If you are facing such an issue, you can solve it by force closing the app on your device and reopening it.

CID-based images on web-mail applications

Some of the web applications do not properly process messages while replying or forwarding. The source code is being modified, therefore the address of the image may be improperly defined. As a result, images are not visible.

To solve this issue, please first try using a desktop mail client instead of a web application. However, if you are unable to obtain or run such software, please try changing the format of the images, as described here, and check if the problem persists.

Unsupported image format or filename

When embedding images to emails and signatures, it's best to use the most common image formats such as PNG or JPG (JPEG), as they are supported by the majority of mail clients. If your embedded pictures are not displaying correctly, check their file format and, if necessary, try converting them to one of the mentioned formats.

Incorrect file names might also prevent graphics from being displayed in emails. We recommend that you only use letters and numbers. Do not use special characters or hashtags (e.g. #myphoto).

Improper image scaling

In some environments, especially those with a higher DPI setting, you may experience problems related to the scaling of images in emails. This issue can be solved by forcing fixed dimensions of the image file. Read this article to learn how to keep the right size of images in your signatures regardless of the mail client/platform.

Outlook image source path conversion


This section applies to users of CodeTwo Email Signatures for Email Clients only.

In Outlook 2013 and later, Microsoft changed the way embedded images in signatures are treated - image embedding was replaced by resource links. If emails contain signatures (added by CodeTwo Email Signatures for Email Clients) with embedded pictures, these signatures are displayed without graphics on the recipients' mail clients. There is one exception - images are only visible if they were inserted from a commonly accessible location. Read this Knowledge Base article to learn how to solve this issue.

If you use Outlook 2016 and you don't see embedded images in signatures, this might also be caused by an old Outlook bug. See this article for details and solution.

Images show up as attachments in Outlook for Mac

In Outlook for Mac, the embedded images might show up as attachments in the final message. In fact, Outlook clients designed to work on the Windows platform are changing the filenames of embedded images on each reply and forward. However, this behavior does not apply to Outlook clients on Macs. Consequently, when CodeTwo software adds an image with the same filename as already existing within a message, Outlook for Mac displays a list of all embedded images in the attachments field. Such a situation might take place e.g. when a signature including an image is added multiple times into the same message.

Images show up as attachments on iOS devices

If you use an iPhone or iPad to reply to or forward an email, images embedded in a signature are sometimes removed from the email body and moved to attachments.

This issue is caused by the email client on your device, and is not related to CodeTwo. Some clients, usually the ones on mobile devices, recognize the path to embedded images in the message body and remove these images, putting them in attachments instead. This behavior helps portable devices reduce mobile data usage (the recipient can choose to download images or not).

Images in email signatures load slowly on mobile devices

If you use Outlook on your mobile (iOS, Android) device, and embedded images load very slowly, this is most probably not related to CodeTwo software. See our dedicated article to learn more.

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