With Mixmax, you can easily share an email with someone when forwarding isn’t an option and copy and pasting is too clunky. When you click the Share button (see the screenshot below), it creates a unique share URL (e.g., https://mail.mixmax.com/m/5m3VxNmUJ75NZdxRa). The ID on the URL is random, so it's nearly impossible to guess.
Anyone with the link can view
Anyone in my domain can view
Only I can view
The default for shared links is Anyone at my Domain.
In addition to controlling who can see a shared link, you can also control the length of time it can be viewed. You can set an expiration date for the link immediately when you create the link in Gmail.