Icon not showing in the menu bar

First thing to try is,

Try the shortcut key,

If it opens an email compose window, then the app is running. All your shortcuts should be working, check here

Coming to the actual issue,

1) If you already have enough apps taking up your menu bar, the Elephas icon may not show up. Since the number of apps on the menu bar is limited.

Please quit a few applications from the menu bar, and it should work.

2) Some users have faced a similar issue (especially during version updates). Uninstalling the app completely and then installing it helped them.

Uninstall the Elephas app, and clean up the data.

Follow this article to clean the data, https://mackeeper.com/blog/delete-software-leftovers-mac/

(or)

you could use CleanMyMac or similar tools.

Finally, install the app.