How to set Inbox by Gmail as the default email client in Safari (macOS)
It's not straightforward, but doable:


Open Safari, install the mailto: extension, then go to Safari &gt; Preferences &gt; Extensions &gt; mailto: &gt; Options &gt; Custom URL and add the following template:

https://inbox.google.com/?to={to}&amp;cc={cc}&amp;bcc={bcc}&amp;subject={subject}&amp;body={body}

Restart Safari
Open Mail, then go to Mail &gt; Preferences &gt; General &gt; Default email reader &gt; Select &gt; Safari


And you are done! Any mailto: link will now open the Inbox composer.