As another precondition, in addition to sending the patch mail to yourself for review before sending it to the mailing list, it would be nice if submitgit would require the Git tests to have passed.
For this to work, the git/git project at GitHub would need to integrate e.g. with Travis CI (some work for this already seems to be done here) and submitgit would only enable the "Send" button on "The Mailing List" tab if CI reports Git to build and test fine.
This would be particularly useful for people like me who work on a fork of Git for other OSes than Linux (in my case it's the Windows fork) to check whether tests also still pass on Linux.