I am sending bulk html emails, and have the proper "unsubscribe" option at the bottom. If someone forwards such an email, I would like to omit that unsubscribe notice. This is acceptable for two reasons: (1) the forwarded email is no longer a bulk email but rather an email from one person to another; (2) it makes no sense for the second recipient to try to unsubscribe, because they are not subscribed.
There is article describing the situation at https://litmus.com/blog/preventing-unsubscribes-in-forwarded-emails, which also gives a brilliant solution. While that solution may have worked back in 2013 when proposed, it no longer works.
The solution was to take advantage of the CSS cascade and the fact that forwarded html emails often get a <blockquote>
tag right after the body. Thus you could set up selectors such as the following:
blockquote .original-only {display: none !important}
The problem is that forwarded emails have both external and internal stylesheets stripped out. And inline styles cannot take advantage of the cascade.
Is there a modern, workable solution?