In answer to your question, this is a multifaceted problem that comes down to: what do I use email for and how else can that work.
I had already mostly switched from email to instant messaging (Facebook, WhatsApp, SMS, Riot.im, etc.). These have some of their own problems but that's a different discussion so the remaining use-cases are:
- open source code mailing lists: Github issues, dependent on adoption but most seem to have moved here
- private company PM emails: many moved to Slack which I detest, or an issue tracker which is not so bad, or other dedicated PM software. There's usually not much individual choice here though unless you're running the company.
- newsletter updates: these typically come from services like MailChimp so using non-Google email to receive these is fine.
- account confirmation: highly dependent on adoption but SMS is becoming an alternative here often
- official correspondences: job applications, etc. There is no alternative. Possibly a space with room for disruption but it would be incredibly challenging.
Generally though, many options sub a federated technology with a lot of user choice (email) for a centralised walled garden. While I'd recommend Riot.im for the messaging part, my main comment here would be that it would be nicer to just have a built-in email client feature or plugin that alterted you in an obvious manner to the service you were communicating with (doing lookups on the To:/Cc:/Bcc: fields before you send. AND a not-just-for-geeks viable alternative to Gmail that could gain ground over time.