[Tutor] Announcement: recent change in mailing list config

[Danny Yoo]

Hi everyone,

I've recently adjusted the configuration of the Mailman software that
maintains the Tutor mailing list: now only subscribers can post to Tutor.

Previously, the software would stop suspicious "spam" looking messages,
but it would still allow people from outside to post with little
restriction.  This was great because it was casual for people from outside
to post to Tutor.  Unfortunately, it's hasn't been so great because
spammers have been hitting us.

I should have announced this change earlier on the Tutor list, and I must
apologize for making the change so abruptly.  The configuration change
does make the list more closed, and does make certain things more annoying
for people.  On the other hand, we shouldn't see spam any more.

Again, my apolgies for the inconvenience.