Messages in HTML format often include links to external pictures or sounds on the Internet. This technique is often used by legitimate senders who want to avoid embedding large graphics in the message itself.
However, a junk e-mail sender or spammer can use this same capability as a "Web beacon" that collects your e-mail address. When you open the message and the linked content is automatically downloaded, you are also inadvertently verifying to the sender that your e-mail address is a valid one. The sender can then sell your e-mail address to other spammers, with the probable result that you will receive still more junk messages.
What Outlook does to help protect your privacy
To combat Web beacons, Outlook is configured by default to not automatically download pictures and other linked content from the Internet when you open or preview a message.
When Outlook blocks automatic picture downloads in a message, the InfoBar (InfoBar: Banner near the top of an open e-mail message, appointment, contact, or task. Tells you if a message has been replied to or forwarded, along with the online status of a contact who is using Instant Messaging, and so on.) above the message body informs you of the blocking action.

Areas in the message where blocked pictures would appear display a red X placeholder instead, along with explanatory text.

Note E-mail messages that are sent from or to e-mail addresses and domain names that appear in the Junk E-mail Filter Safe Senders List (Safe Senders List: A list of domain names and e-mail addresses that you want to receive messages from. E-mail addresses in Contacts and in the Global Address Book are included in this list by default.) and Safe Recipients List (Safe Recipients List: A list of mailing lists or other subscription domain names and e-mail addresses that you belong to and want to receive messages from. Messages sent to these addresses will not be treated as junk e-mail.) are treated as exceptions, and their linked content is downloaded instead of being blocked.
One of the advantages of blocking automatic picture downloads is that you can avoid viewing potentially offensive material (when external content is linked to the message). Also, if you are on a low-bandwidth connection, blocking allows you to decide whether a particular image warrants the time and bandwidth that are required for downloading it.
Warning messages
When you attempt to forward, reply to, or edit a message that contains links to external content, Outlook is configured by default to display warning messages:
- When you attempt to forward, or reply to, a message Outlook displays the following warning by default.

Do one of the following:
- Click Yes to allow the external content to be downloaded.
- Click No to prevent the external content from being downloaded.
- Click Cancel to return to the message.
- When you attempt to edit a message Outlook displays the following warning by default.

Do one of the following:
- Click OK to allow the external content to be downloaded.
- Click Cancel to prevent the external content from being downloaded.
You can turn either of these warnings off by selecting the Please do not show me this dialog again check box, but this is not recommended.
If you have already turned these warnings off, and you want to turn them back on again, do the following:
- On the Tools menu, click Trust Center, and then click Automatic Download.
- Select the Warn me before downloading content when editing, forwarding, or replying to e-mail check box.
Note If you print a message that is linked to content that has not been downloaded automatically, the blocked content is downloaded and does appear in the printed message.