Over the years, it has become more difficult to properly work with the Gmail web interface. Since the Gmail upgrade in 2018, it is no longer possible to open a Draft compose window automatically. The app now opens the Drafts summary list.
In January, 2019, I was notified that the requirements for widely using the Gmail API drafts compose permission were becoming more rigorous, including an annual third-party security audit. I expect that will require more effort and funds than I am willing to spare for the application.
So, you should expect that this application will quit working some time around the end of 2019. After that time it will still be possible to set up to authenticate on an indivdual basis (without the audit) by modifying the Google account referenced in the source code.
This is the development home for the Linux gnome-gmail package. It allows desktop mail actions, such as "Send File as Email" or web 'mailto' links, to be handled by the Gmail web client.