What is this <URL: ... > stuff?
Your URL has been word-wrapped/mangled in some other fashion in a message, and doesn't work when I click on it.
This is the Frequently Given Answer to such questions and statements.
The appendix to RFC 1738 defines a syntax for URLs sent within "plain" text in messages, whereby a URL is preceded by the five characters <URL: and succeeded by the single character >. This is what you are seeing. In theory, either your Mail User Agent or News User Agent, or you yourself, can extract the URL thus encapsulated and use it to find the referenced object. And, indeed, if you are "clicking on" a URL in a message, your MUA/NUA is attempting to make it easy for you to do just this.
This syntax isn't robust. There is simply no way to robustly delimit entities such as URLs within free-form "plain" text. There's no way to reliably distinguish between entities and text that just happens to resemble them. This is, after all, why we have text-with-markup formats in the first place.
MUAs and NUAs usually don't understand this syntax properly. Although they might attempt to be "user friendly" and turn URLs within "plain" text in mail messages into hyperlinks that one can select, they don't do a very good job of it. Some just look for the < and the > and forget about the URL:. Many cannot cope with line breaks or other whitespace in the middle of URLs (despite what RFC 1738 says) and so truncate them, rendering the resultant hyperlink incorrect.
MUAs and NUAs sometimes break this syntax. When sending, quoting, or forwarding messages they will insert line breaks (and sometimes other characters) within URLs, triggering the problems mentioned before when other MUAs and NUAs come to display the resultant messages, with the URLs as hyperlinks.
It is all too easy to encounter these problems in practice.
For example: This affects the URLs of Frequently Given Answer pages. The encapsulated URL <URL:http://homepages.tesco.net./~J.deBoynePollard/FGA/mail-url-style.html> is 76 characters long. That is longer than some peoples' and some softwares' choices of word-wrap boundaries. People have experienced problems with the encapsulated URLs for Frequently Given Answer pages being mangled, when those encapsulated URLs have been quoted several levels deep within mail and news messages.
As such, the RFC 1738 encapsulation of URLs within "plain" text is only usable up to a point. For reliable encapsulation of URLs within messages, that is not subject to the vagaries of quoting and of word-wrapping, it is best to use a more appropriate format for the message, such as HTML.