* [MM-36872] Adding headers for mail threading * MM-36872 Add message id and mail threading headers * MM-36872 Add message id and mail threading headers * MM-36872 Add msgId, inreplyto, references headers * Fixing comment issues * Applying gofmt lint fixes * Applying gofmt lint fixes * MM-36872: Updates required from merge. Co-authored-by: Mattermod <mattermod@users.noreply.github.com> Co-authored-by: Martin Kraft <martin@upspin.org>