Images show as Red X in Outlook: (It may effect all images and all employees):
Outlook cannot show images located on https.
This is caused by a special setting in your Internet Explorer (IE). Even if IE isn't your default browser, Outlook relies on some IE settings.
Reset Internet Explorer to its default setting.
Go to Tools > Internet Options > Advanced (tab) > Reset button (bottom of window).
Or specifically, untick this setting: