Outlook 2007 blocks messages containing a specific URL

Question

Note: This is a self-answered question. It originally received no responses and may appear too broad as a stand-alone question. I discovered the answer myself and am leaving it in place in case anyone else runs into the same problem.

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When attempting to send a message containing a specific URL, the message does not get sent to the addressee. Instead, a message from me, addressed to me, is delivered back to the originating inbox. It contains the original message as an attachment, and that URL is missing from the message body in the attachment.

It happens with any addressee. There is no error message, and everything else works normally.

The computer is running Win 7 Home Premium and Outlook 2007. The problem is specific to this single URL when it is typed into the body of a message as text: http://www.couponpreviews.info (which is a good, safe URL and a normal web site).

The behavior is a little like that URL is being quarantined as malware, but it is only being affected within Outlook (nothing blocks accessing it in a browser, and if I create a file containing it, the file is not quarantined).

If Firefox is used to open that URL, and then the "email link" feature is used, the same result happens (Outlook is the default email application).

As a test, I sent an email containing that URL from another computer to the email address on the affected computer. The message was received but only the "http://" portion of the URL appeared in the body of the message, the rest of the URL was gone.

Whatever is going on is obviously within Outlook, and some process has become associated with that URL. However, there is no Outlook feature designed to work this way. Outlook is virtually unchanged from the "as shipped" version; I have not set up any special rules or filters. Microsoft updates are current.

I've never come across behavior similar to this and an online search turned up nothing.

Anyone have any idea what might be going on?

Answer 1

The process of writing this question triggered a clue to the answer. In case anyone else runs into this situation, here it is.

My third party anti-virus program has an Outlook add-in to check email in real time. It uses web site blacklists as at least one basis for identifying hazardous email content. Sometimes the lists have false positives.

The way it handled "problem" content was to delete the URL from any incoming or outgoing message. Apparently as a way to advise the sender that the outgoing message had not been sent, it returned the message to the inbox, albeit with no explanation. The missing URL was meant to be a clue to the problem.