If you happen to share a link to an email on Facebook, Facebook will usually generate a little thumbnail preview to go along with it. This preview contains an image pulled from the content as well as a the title and some body text.
If, at this time, you notice a mistake in your email, fix it, and go to re-publish it to Facebook, you will often notice that it is not recognising the change you've made.
To get around this, you can add a parameter to the end of the link's URL. This tricks Facebook into thinking it's a completely different link, which will force it to go and re-check the data and thus, display the correct information.
The parameter to add to the end of the link to your email is: