link to the SPF/DKIM issue in the roadmap

it's just one possible solution on the deliverability issue, which
will probably require a TPA-RFC to officialize

roadmap/2021.md

@@ -28,7 +28,9 @@ attention. In general, the over-arching goals are therefore:
    * [ ] systematically followup on and respond to abuse complaints (https://gitlab.torproject.org/tpo/tpa/team/-/issues/40168)
    * [ ] diagnose and resolve delivery issues (e.g. [Yahoo](https://gitlab.torproject.org/tpo/tpa/team/-/issues/34134),
          [state.gov](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40202), [Gmail](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40170), [Gmail again](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40149))
-   * [ ] provide reliable delivery for users ("my email ends up in spam!")
+   * [ ] provide reliable delivery for users ("my email ends up in
+         spam!"), possibly by following newer standards like SPF,
+         DKIM, DMARC... ([issue 40363](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40363))
    * [ ] possible implementations:
      * [ ] setup a new MX server to receive incoming email, with
            "real" (Let's encrypt) TLS certificates, routing to