Cannot view pictures in signed email using Outlook for Windows

Microsoft has tightened the security settings in Outlook for Windows by blocking external content in S/MIME encrypted and signed messages by default. User used to have the option to download external image in email messages can no longer choose the options in signed message.

Blocking external content in email messages prevents your computer from downloading malicious files and scripts, and it protects your privacy by stopping web beacons from tracking when you open an email message.

If you use Outlook in Windows and would like to download external content in encrypted or signed messages, please follow the steps below (be aware that the external content might be malicious) :

1. Open Outlook.
2. From the File tab, choose Options.
3. Select Trust Center, and then Trust Center Settings.
4. Select Automatic Download.
5. Uncheck Don’t download pictures in encrypted or signed HTML messages.  
6. Click OK to save.

Enabling this option won't make Outlook download external content by default and you can still determine whether to download external contents in each of the signed email messages.