Great tutorial. You may want to add a section about using git-format-patch to allow one to see the emails on disk and using git-send-email with those files. You may also want to add a caveats section about certain email providers.

In my experience, any Microsoft Exchange/O365 server will most likely mangle the email server side (introducing quoted-printable encoding characters or changing the message-id field. Gmail will require that you enable insecure application access in order to use git-send-email. If you don't do that, then using git-send-email will result in a authentication failure error (which you can see if you use the --debug flag).