Hotmail has bounced many connections with a 'fatal' error code: 550
SC-004. This happened at about 0015 on 19 March (UTC).
Looking at Hotmail's error page at:
http://mail.live.com/mail/troubleshooting.aspx#errors says it was
rejected for "Policy reasons"
The result is many (all?) hotmail users have been 'disabled' in the
mailing list.
List users can reactivate themselves at
https://lists.wikimedia.org/mailman/options/wikimedia-l
Regards, Richard.