If you have HTML rendering turned off, you will see the gibberish.
You should have HTML rendering turned off. Otherwise the HTML could exploit a security vulnerability in your email program and access your system. At the very least, it could have you downloading content from a page you did not wish to hit.
If you turn off HTML rendering, the HTML will be delivered as an attachment. If you really need to read it (sent from someone who formats their outgoing email in HTML) you can always read it when disconnected from the internet. That way there is no possibility it will hit a Web page without your permission.
If you have the option, you should format your outgoing mail in plain text rather than HTML so others can read your email with HTML rendering turned off.
Just my $.02.
Shalom.
In many cases, the URL will also contain encoded information to tell the spammer that your email address is "live" (i.e., someone is reading it and doesn't have a particularly good spam filter).