If you’re not using the stock mail app it might be built-in. Mailplane and Kiwi, for example (both for Gmail,) appear in the pop-up right-click Share menu in the Finder.
in mojave you can use the quick action in the finder and link that to an automator action to send the email with the selected files attached.
I have one like that on my system.
create quick action in automator -> action receives files and folders in finder -> create new email -> add files to email in foreground -> done
or when you have Keyboard Maestro you can create a shortcut to do exactly what you want.