I'm not receiving some "html" formatted e-mails.
The Exchange server has anti-spam software that is removing all e-mail that appears to be a "web beacon". Web beacons are html formatted e-mails that force content to be downloaded from the web, and in spam e-mail it can act as what is known as a "Web beacon," by telling the sender that the e-mail address is valid - a technique used by spammers. Viewing the message in a preview pane without opening it is enough to trigger the Web beacon.. The beacon can lead to more unwanted mail from the original sender and, potentially, from other spammers who have access to the same mailing list. It is estimated that between 70 and 80% of spam today uses this technique. If you think you have e-mail of this type being blocked, you should contact the sender and ask them to send you the information in plain text.

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