Debian packaging is considered experimental!
You first need to generate a changelog, then create a .deb
package.
scripts/create-debian-changelog.py #May take some time
debuild -us -uc -b
The first command generates changelog messages for all git commit messages. If you're not interested in a proper changelog, you can use this command instead of create-debian-changelog.py to create an empty changelog:
dch --create -v 0.0.0-dev$(git rev-list $(git rev-parse HEAD) | wc -l) --package mailpile ""
debuild -us -uc -b