Privacy basics - Thunderbird
By default, Thunderbird blocks remote images and other content in messages from people you don't know. This protects your privacy because spammers can verify your email address by detecting if you viewed a remote image in a message from them. Its also possible to embed an executable (malware) in images.
When you receive a message with remote images, Thunderbird will display an alert stating that remote images have been blocked, and the images in the message body will be replaced with simple place-holders (screenshot). If you do want to view the remote images—for example, if you subscribe to an e-mail newsletter that regularly includes remote images—all you need to do is click the "Show Images" or "Load Images" button that appears to the right of the alert message.
Thunderbird 1.5 defaulted to loading remote images from people who are in your Personal Address Book. Thunderbird 2.0 and later versions blocks all remote images by default. You can display remote images whenever you read a message from a specific sender by clicking on "Click here to always load remote images from ..." in the e-mail message, as shown below:
Doing this adds an entry to the address book that has the "Allow remote images in HTML mail" option checked for the specific sender. You can also change this option for an address book entry by going into the address book, looking at the properties for an entry, and selecting/deselecting the "Allow remote images in HTML mail" option. Unfortunately, you can only do this for one address book entry at a time.
You might want to create a images address book and select it instead of the personal address book if its for a newsletter to which you can't reply.
Its possible to display all images from any sender, though its not recommended since malware can be embedded in images, and spammers will be able to verify your e-mail address. If you want to do this use the Config editor to toggle the preference mailnews.message_display.disable_remote_image to false.
A better alternative would be to use the Config editor to create a mail.trusteddomains setting that specifies what e-mail domains it should automatically display remote images for. This is much easier than having to specify each email address, but you're taking the risk that you won't get any messages with a spoofed From: header in one of those domains. The setting contains a list of domains separated by commas, with no wild cards, white space or subdomains allowed.
- mozillazine.org is okay
- mozilla.com,mozilla.org is okay
- *.mozilla.com is invalid
- mozilla.com, mozilla.org is invalid
- forums.mozillazine.org is invalid