By default, Outlook for Mac doesn't automatically download pictures or photos in email messages if the images are stored on the Internet. You might see blue question marks in your mail like this:
However, you can turn off this preference.
Start the Outlook client.
Select Preferences from the menu bar.
Click on the Reading entry.
On the Reading page, select “In all messages” for “Automatically download a picture from the internet” under the Security section.
Save the changes and exit the Preference window.