What does HackerNews think of bower?
A curses terminal client for the Notmuch email system
As a bonus, it's written in a fairly niche programming language: mercury, which is a strongly typed prolog dialect.
I personally use mbsync[3] to pull my email into a local maildir. I also use notmuch[4] and a nice tui[5] to search, read and write it. Note that filenames in maildir are unique, but provide little value beyond that. Some emails are also encoded in ways that will hide content from grep and friends (base64 being among the most popular ones). This makes notmuch especially valuable, as it abstracts all those encoding issues away and provides an amazing search interface.
I do not use a git repository for email myself, yet since a maildir is just a directory tree of plain text files, storing it in a repo is a no-brainer:
mbsync -a # Configured via dotfiles
cd my_local_maildir
git add .
git commit
[1]: https://en.wikipedia.org/wiki/Mbox[2]: https://en.wikipedia.org/wiki/Maildir