In my question and answer application, Joe signs up, logs in and adds a question. He then shares the question via email to his trusted friends.
How safe is it to provide a link within that app generated email to allow his friends to directly respond to the question without having to register on the site?
The key goal is that I would like the user's friends to be able to respond to his question without having to register on the application site. Assume that the link embeds the email id of the receiver, so the app can map each response to the email id that initiated that link.
What precautions do I need to include to avoid or detect malicious clicks on that link?