Is this a scam or is it for real?

[Karl Berry]

    Subject: Is this a scam or is it for real?

Hi Rolf - it is real. Your email address was/is rejecting mail from
tug.org, so mailman eventually gave up and marked your address as
undeliverable. (It's surprising that you received this message, since it
too was sent from tug.org, but the ways of mail filtering are
unfathomable nowadays.)

The actual smtp error was:
    <r.turner at auckland.ac.nz>
    (reason: 550 csi.mimecast.org Poor Reputation Sender. -
    https://community.mimecast.com/docs/DOC-1369#550
    [6FzhYkwMOUm1dBVUyVadBA.au23])

I suppose your university uses mimecast for mail filtering. I cannot
guess why mimecast thinks tug.org has a "poor reputation". No url is
given for administrators (me) to request amelioration, so there's
nothing I can do. Maybe your university sysadmins can do something, like
request tug.org be removed from mimecast's blacklist. 

    Would I expose myself to danger by replying to the messages
    as suggested?

No, but it won't help, either, since messages from texhax will continue
to be blocked for you until mimecast undoes our "poor reputation".
(If you have an alternate email address, you could subscribe there.)

    I am disturbed by the fact that my members password is given "in plain"
    in the message.  Surely this is a security risk 

Yes, but that is how mailman has always operated. And this is why people
should never use mailman passwords for anything else. (By default they
are randomly generated.)

The mailman maintainers are well aware of the issue, though I don't know
if they will ever do anything about it. I can't redevelop mailman myself.

Predating the web, it was common to do all kinds of interactions over
email (and long predating any kind of encrypted email). 

    Please reply to me directly rather than via the list, 

Well, I'll also cc the list since this whole issue is becoming
unfortunately common nowadays. tug.org often (and randomly) gets
blacklisted, causing all kinds of mail bounces. It is a big
time-consuming headache for me.  --best, karl.