Hot Conversations alert you by mail when an email has been opened many times over a short time period.
Why is this useful?
If the recipient has opened your mail many times over a short time period then this may mean that they are very interested in the contents of the email (either they are reading the mail many times themselves or they've decided to forward the mail to other people).
Enabling/disabling Conversations.
Hot Conversations can be enabled/disabled in your Mailtrack settings.