If you are writing an email and you want to track a link but don't want to use InboxCast, you can simply add a parameter to the end of the link. The parameter to add is _clde=email.
Here is an example of what your link should look like: http://www.clickdimensions.com/tour/?_clde=bob@fakecompany123.com
After the recipient clicks your link, all his or her browsing on your site will be tracked; even if they've never previously been to the site. Of course, the email address you include in the link will already need to be in your environment in any of the three Contact or Account email fields. This link format works regardless of where it comes from. You could message the link to the person, embed it in a PDF or other document and it would also work. But, remember, the link is specific to the person whose email is in it.