staging appears to be receiving new data
If you look at staging, you'll see that there are some new comments from the community (e.g. https://staging.gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2408#note_34999336).
Unless that user actually logged into staging (which I didn't think was possible), my guess would be that mailroom is pulling from the same reply-by-email queue.
@jarka mentioned that @tmaczukin noticed this too.
While it's nice that we are testing that reply-by-email actually works with the production mailbox, I think we might want to have a separate inbox for that on staging.