[ori_b]

Many local mail clients also just let you pipe the message into a command; for example, in mutt, you could just type:

   |git am

once you have the message open.

[jen20]

You may have a skewed idea of “most” here.

Most people are using gmail, but when it comes to local clients, Outlook, Apple Mail and Thunderbird are by far the most common and as far as I know none of them support this without extra steps.