When you open an email message that contains images in Microsoft Office Outlook, the image areas are blocked. These areas display a red "X" placeholder. Blocking pictures can help protect your computer. Microsoft Outlook is configured by default to block automatic picture downloads from the Internet. You can, however, unblock pictures that you think are safe to download.
Unblock picture downloads for a single message
You can unblock downloads of linked pictures and other external content for a single message that comes from a trusted source.
Choose the InfoBar at the top of the message, and then click Download Pictures.
Download Images for All Incoming Messages (not recommended).
In Outlook 2019, 2016, 2013 and 2010 simply go to File > Options > Trust Center > Trust Center Settings > Automatic Download and then uncheck “Don’t download pictures automatically in HTML e-mail messages or RSS items”.
If you’re using Outlook 2007, go to Tools > Trust Center > Automatic Download and then uncheck “Don’t download pictures automatically in HTML e-mail messages or RSS items”.
For Outlook 2003, go to Tools > Options > Security tab > Change Automatic Download Settings > and then uncheck “Don’t download pictures or other content automatically in HTML e-mail”, and also uncheck “Warn me before downloading content when editing, forwarding, or replying to email”.
Unblock Images from a Certain Domain or Email Address
To execute this method to allow images from a trusted source or a specific domain you, have to follow the two-step procedure and this helps you to fix ‘images not displaying in Outlook 2016’
Initially, you have to right-click on the Blocked components. To do so, you have to open the message received from a trusted source and domain.
After that, hit a click on Add the Sender into Safe Senders List then, add the YYY@domain to Safe Senders List.