Buttons such as Track and Set Regarding are missing in Dynamics 365 App for Outlook

When opening the Dynamics 365 App for Outlook using Outlook desktop or Internet Explorer, icons for buttons such as Track and Set Regarding are missing. The buttons still function but the visual icons are missing. If you open the app in another browser such as Edge or Chrome, the button icons do appear.

NOTE: If the Track and Set Regarding options are completely missing, see the following article:

Track and Set Regarding options are missing in Dynamics 365 App for Outlook

https://support.microsoft.com/help/4462486 

This issue can occur if your Internet Explorer security settings are configured to not allow font downloads.

NOTE: If you use Outlook desktop, it always loads web pages using Internet Explorer even if you have other browsers installed.

If the symptoms match what is described in the Symptom section, try the following resolution:

1. Open Internet Explorer.
2. Click the gear icon in the upper-right corner and then click Internet Options.
3. Click the Security tab.
4. Select the security zone used for your Dynamics 365 URL and then click Custom level. 
5. Scroll down to the Downloads section to find the setting Font download and verify it is set to Enable.
6. Click OK.
7. Close and reopen Outlook.

If the steps above do not resolve the issue, refer to the following Blog post that discusses other potential causes for font icons not appearing in Internet Explorer:

https://blogs.msdn.microsoft.com/askie/2017/08/30/windows-10-with-internet-explorer-11-some-website-graphic-icons-are-missing