Knowledge Base

Signature preview not working in Outlook

This article concerns CodeTwo Email Signatures for Office 365 Add-in, which has been deprecated and will be retired in Q3 2024.

Switch to our new add-in, CodeTwo Signatures Web Add-in for Outlook, as soon as possible to ensure smooth and uninterrupted experience. The modern Web Add-in allows users to preview their cloud (server-side) signatures, and it can also add signatures directly to emails in Outlook for Windows, Outlook for Mac, OWA, and mobile Outlook (iOS, Android). Learn more


You experience problems with CodeTwo Email Signatures for Office 365 Add-in in Outlook and Outlook on the web (OWA). For example, the add-in button does not appear in the new email window, is inactive (Fig. 1.) or, in general, the add-in does not work as expected.

Fig. 1. Inactive add-in button in the Outlook’s new email window.


Since signatures are added in the cloud, they are added even if the preview add-in is not deployed or does not work.


Issues with CodeTwo Email Signatures for Office 365 Add-in can be caused by several factors. Follow the links below to find a solution that works best in your environment:

Multiple add-ins installed on the same client are incompatible with each other

There are several types of Outlook add-ins, and some of them might interfere with each other. Older types of add-ins, such as COM add-ins, can be incompatible with newer types of add-ins, such as web add-ins. CodeTwo Email Signatures for Office 365 Add-in is an example of a modern web add-in and – unlike COM add-ins – it does not install any code on your machine.

In rare cases, you may need to disable a COM add-in, especially if it uses custom forms, for CodeTwo Email Signatures for Office 365 Add-in to work properly.

To find out which COM add-in causes the issue, you first need to disable all the COM add-ins that you installed (you don’t need to disable the add-ins that are installed by default by Microsoft, such as Microsoft Exchange Add-in) and then enable them again one by one. Remember to restart Outlook after re-enabling each add-in and check if CodeTwo Email Signatures for Office 365 Add-in is active.

To disable and re-enable a COM add-in:

  1. In Outlook, go to File > Options > Add-ins.
  2. In the Manage section at the bottom of the window, choose COM Add-ins and click Go (Fig. 2.).

Fig. 2. Selecting COM Add-ins.

  1. In the window that opens, clear (deselect) the checkboxes for the add-ins that you want to disable and click OK. (Fig. 3.).

Fig. 3. A list of Outlook COM add-ins. To disable an add-in, clear its checkbox.

  1. Re-enable the disabled add-ins one by one by selecting (checking) them again and restarting Outlook each time to see if the signature preview is working.

After finding out which add-in is the source of the problem, disable it whenever you want to preview your signatures.

You are not able to launch the add-in (This add-in could not be started)

When you start the add-in, instead of the signature preview you see the following error in the add-in pane (Fig. 4.):

This add-in could not be started. Close this dialog to ignore the problem or click "Restart" to try again.

Fig. 4. The signature preview does not launch.

This issue might occur if Protected Mode is disabled in your Internet security settings in Windows. To solve this problem, try the following:

  1. Launch Internet Explorer, click the Tools button and select Internet options.


    You can also access these settings from the Windows Control Panel or by opening the Start menu, typing Internet options and pressing Enter.

  2. Go to the Security tab and select the Internet (default) zone.
  3. Select the Enable Protected Mode checkbox, as shown in Fig. 5.

Fig. 5. How to enable Protected Mode in the Internet zone.

  1. Restart Outlook (and Internet Explorer, if necessary).
  2. If the problem still persists, try enabling the Protected Mode in the Restricted sites zone and restarting Outlook.

CodeTwo domain is blocked by antivirus software

To display a preview of the signature, CodeTwo Email Signatures for Office 365 Add-in needs to access two web locations:

Your antivirus software may be set to block connections to any domain outside its list of trusted domains. Make sure that you add the IP address of your Azure region and the address of the add-in to trusted domains in your antivirus software.

Your Outlook version is not supported

CodeTwo Email Signatures for Office 365 Add-in works with all 32- and 64-bit versions of Outlook 2013 and newer. However, to use this add-in in Outlook 2013, you need to update Outlook 2013 to the newest version.

The add-in also works with Outlook 2016 for Mac and Outlook on the web (OWA). See the full list of supported versions of Outlook

The add-in pane is not pinnable

By default, the CodeTwo Email Signatures for Office 365 Add-in pane disappears every time you compose another email and you have to open the add-in from the ribbon to see the signature preview. To avoid this and keep the add-in pane open, you need to pin it to your Outlook via the button shown in Fig. 6.

ESIG for O365 add-in pinning
Fig. 6. Use the highlighted button to pin/unpin the signature preview pane in Outlook.

The availability of the option to pin add-ins depends on your Outlook version. If you don't see the pin button (Fig. 6.), you might need to update Outlook.


Pinnable add-ins are available in the Click-to-Run versions of Outlook 2016 (build 7668.2 or later for users in the Current or Office Insider Channels, build 7900.x or later for users in Deferred channels). Learn more

Images are not displayed by the add-in

You experience the following problems when using the signature preview add-in in Outlook and Outlook on the web:

  • your signature includes pictures and other elements, and some/all of these pictures are not visible in the signature preview pane;
  • your signature contains pictures only, and the add-in is not able to generate the signature preview (it's loading endlessly) or shows an error instead of your signature (Fig. 7.).

Signature preview error
Fig. 7. The add-in might not generate the signature preview if your signature includes images only, and these images are incorrectly defined in the signature's source code.

First, you need to make sure that your images are correctly inserted into the signature. To check your signature:

  1. Sign in at and select your signature rule.
  2. Go to the Design step and open (edit) your signature to launch the signature editor.
  3. In the editor, click the </> HTML source button on the ribbon to view the HTML source code of your signature.

If your image is inserted inside a paragraph (<p>) tag directly in the <body> tag (not inside any table), the preview will not load and you will get the error shown above (Fig. 7.) or – if your signature contains other elements – the add-in will show everything except the image (Fig. 8.).

Fig. 8. An image is not previewed if it's inside the <p> tag directly in the HTML body.

This is a known issue. To fix it:

  • remove the <p> tag so that only the <IMG> tag remains under the <body> tag (Fig. 9.)

    Fig. 9.  An image is placed directly (without the <p> tag) in the HTML body of the signature.

  • or put the <p> tag with the image inside a table (Fig. 10.).

    Fig. 10. The <p> tag that includes an image is placed inside a table.

Add-in is not showing up in Outlook Version 1909 (Build 12026.20334) or newer

CodeTwo Email Signatures for Office 365 Add-in is installed per Office 365 user, not per device, so it allows users to automatically preview signatures in Outlook, Outlook on the web and Outlook for Mac. However, in Outlook Version 1909 (Build 12026.20334) or later, you might need to enable the Allow the use of additional optional connected experiences in Office 365 option in the Trust Center to be able to see the CodeTwo add-in.

To enable this option:

  1. Open the Group Policy Management Editor.
  2. In the editor, go to User Configuration > Policies > Administrative Templates > Microsoft Office 2016 > Privacy > Trust Center.
  3. In the Trust Center, right-click the Allow the use of additional optional connected experiences in Office setting (Fig. 11.) and click Edit.

Allow the use of additional optional connected experiences in Office.
Fig.11. The Allow the use of additional optional connected experiences in Office setting.

  1. Enable the option, then click Apply and OK.
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