Basically if you use the Send Email link shown when you are editing a test case to send an email to anyone it shows the content of the email in the History and Notes. There is no way to disable this behavior or make it optional.
Normally when you send someone a link to anything in any other application it simply sends it to that person as an email. It does not put the email itself in anything like History, etc.
Ideally there should be a way to: \
- enable/disable this behavior, and/or
- on sending of the email, optionally tick "Record in Notes/History" (disabled by default)
IMHO, the current behavior is peculiar and unexpected.
Here you can review submitted feature requests and vote up the ones you like! If you can't find the feature you want - go ahead and suggest your own idea. Ideas with the highest rating can be implemented in the product.