Changing the default mail app without signing into Apple Mail

In macOS, you can only change the default mail app in Apple Mail’s Preferences, but you can only get to Mail’s Preferences if you sign-in to an existing email account. Here’s a trick to workaround that.

You probably got stuck here —

You can skip all this sign-in business with a single command in Terminal. Tested and known to work on at least 10.13 and 10.14.

If you want to set the default app to Open In Webmail

If you want to set the default app to anthing else…