There isn't. Something like that would have to be feature specific because the page is just a container for feature instances, it doesn't have any knowledge of content changes within features.
However, features can (and some do) update the LastModifiedUTC field on the mp_Pages table but there is nothing in mojoPortal to track that or send emails. Something like that could possibly be implemented with custom code, such as a database trigger that could be added to the table to detect updates and which could send an email.
Generally what I do on this site is a bit more manual, I keep a list of new or updated documentation and then I link to those in our monthly newsletter which is sufficient for my purposes.