With emails it is the sender who has the most control over what emails are sent and the recipient has less control.
The entire concept of spam filtering to try to strip out junk emails that are not wanted is one indication of this difference.
For this reason the vast majority of people have the security settings in their email program set much higher than they have set in their browser.
This higher setting usually means that they have their email program set up to ignore any Java Script that might be found in the email.
Of course the reason why most HTML emails don't contain Java Script because they don't have any need for it.
Why then so we not see Java Script used in HTML emails?
The answer to this relates to a fundamental difference between web pages and emails.
With web pages it is the person browsing the web who decides which web pages that they visit.
A person on the web is not going to visit pages that they believe may contain anything that might be harmful to their computer such as a virus.
By Stephen Chapman When writing an email the two main choices that you have are to write the email in plain text or to use HTML.
With plain text all you can place in the email itself is text and anything else must be an attachment.