Peer4commit and spam

There was a complaint about peer4commit sending spam to project contributors: https://github.com/sigmike/peer4commit/issues/102

What do you think we should do to prevent such a thing from happening again?

May be all recipients should be registered on peer4commit with an option to opt-out from mail notification?

Add a link in the email : Click here to stop getting these email for this project or for peer4commit.