Can be various reasons. The obvious one you seem to have checked out which is the image contains remote content and is by default blocked. Usually, you would see a message just above the content explaining remote content blocked. If you view an email in plain text mode then the image is usually added an as attachment instead, but using the setting 'View' > select 'Display attachments inline' will show images. If using Plain Text then try View > Message Body As > Original HTML. If the message has been marked as Junk, then they will have been "sanitized", meaning that they are displayed without any images or other HTML formatting. You need to select the 'not Junk' to have email put back in Inbox. IT is possible your anti-virus was scanning the email when downloading and caused an issue, suggest you switch off AV from scanning emails. You could test if this is the issue by restarting the computer in 'Safe Mode with Networking' and then starting Thunderbird. See if setting this setting works which can help if headers not totally correct. Info at link below regarding checking the headers. Menu app icon > Options > General scroll to the bottom and click on 'Config Editor' button in search type: : parts Locate: mailnews.display.show_all_body_parts_menu If set to 'False' double click on like to toggle calue to 'True' Info here: http://kb.mozillazine.org/Images_in_messages_do_not_appear