Q: Is there a way in Microsoft Outlook to allow some HTML messages to automatically download images but still block others from doing so?

A: I was asked this question at the Angelbeat seminar (http://www.angelbeat.com/) in Las Vegas in October 2010. The person who asked the question wanted to store images on a network share so they didn't have to be sent within the message itself, and then have them referenced in the HTML and rendered from a trusted location.

For several versions now, Microsoft has, by default, prevented the automatic download of embedded images in HTML email messages received in Outlook. But there is indeed some granular control over which images are blocked and which are allowed, depending on the source of the message and the download source of the images.

In Outlook 2010 and Outlook 2007, you control these settings in the Trust Center. You can access the Trust Center in Outlook 2007 through Tools, Trust Center; in Outlook 2010 you select File, Options, Trust Center, then select Trust Center Settings. You can also open this dialogue box by right-clicking the information bar (the warning text that might appear between the Ribbon and the message sender and recipient information in a message with blocked content) and selecting Change Automatic Download Settings. Figure 1 shows the Outlook 2010 Trust Center Automatic Download options window. These options provide a few ways of allowing images to appear in email messages while still blocking images from unknown sources.

Figure 1: The Trust Center Automatic Download options window in Outlook 2010

As an example, I've opened a message from Twitter informing me of a new follower for my Twitter account. As Figure 2 shows, the images are blocked by default.

Figure 2: An email message showing blocked images

In Figure 1, you can see that the setting Permit downloads in e-mail messages from servers and to recipients defined in the Safe Senders and Safe Recipients Lists used by the Junk E-mail filter is selected. If I add the sender address for the Twitter alert in Figure 2 to the Safe Senders List, the images within that message are automatically downloaded—as reflected in Figure 3! Also in Figure 1, you can see in the other options that the same principle applies to messages with content from website URLs added to the Trusted Zone in Internet Explorer, to RSS feeds if allowed, and to SharePoint Discussion Boards.

Figure 3: The message after images have been downloaded because the sender was added to the Safe Senders List

Remember, to add the sender to the Safe Senders List, right-click the message information bar and select Add Sender to Safe Senders List, or Add Domain to Safe Senders List to include all addresses from that domain. Now, if you have an automated email from a monitoring application, for instance, with pretty charts and graphs within the message, you can add the sending address to the Safe Senders List to automatically present that content in messages.

These settings controlling automatic downloads are saved in the registry, although the keys don't exist until the defaults are changed. Figure 4 shows the different keys that map directly to the options listed in Figure 1. As registry keys, they're easily managed by administrators through Group Policy, logon scripts, or other centralized administration tool.

Figure 4: Registry settings for managing automatic download settings

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