https://knowledgebase.constantcontact.com/articles/KnowledgeBase/5554-images-not-displaying-in-an-email-client?lang=en_US
Images Not Displaying in an Email Client
Outlook 2016
- To unblock picture downloads for all messages in Outlook 2016:
- Click File.
- Click Options.
- Click Trust Center.
- Under Microsoft Outlook Trust Center, click Trust Center Settings.
- Uncheck the Don't download pictures automatically in HTML e-mail messages or RSS items check box.
If this doesn't resolve your issue, check if you have text only emails enabled:
- Click File.
- Click Options.
- Click Trust Center Settings.
- Click E-mail Security.
Under Read as Plain Text, make sure that the Read all standard mail in plain text is unchecked.