mails relayed from lists.tpo to gmail.com bounces

It seems we're having trouble relaying mails to gmail.com and possibly other providers.

A similar question was raised by a tor-announce@ participant in Message-ID: <CAHQQdjtuVj68EVw_TsnDGiTRj1bY7iyxuehUDj6bya=KAqE0MQ@mail.gmail.com>

I myself had trouble sending mail to a @tpo account that is forwarded to gmail (bounce is Message-ID: <20190311210933.9AB57E1B16@eugeni.torproject.org>):

<target@gmail.com>: host gmail-smtp-in.l.google.com[64.233.167.26] said:
    550-5.7.1 This message does not have authentication information or fails to
    pass 550-5.7.1 authentication checks. To best protect our users from spam,
    the 550-5.7.1 message has been blocked. Please visit 550-5.7.1
    https://support.google.com/mail/answer/81126#authentication for more 550
    5.7.1 information. f2si4120705wrj.403 - gsmtp (in reply to end of DATA
    command)

I suspect this might have to do with (lack of) SPF records and/or ARC headers.