Yahoo keeps losing my email!

I have clients and friends with yahoo-hosted email accounts.
Mail I send to @yahoo.com addresses never arrives, and I don't get bounce messages either.
Mail to other addresses hosted by yahoo bounces:
<munged@supergenius.com> : host
mail1.wss.vip.scd.yahoo.com[ 66.218.85.170 <http://66.218.85.170>] said:
550 5.0.0 <munged@supergenius.com >...
RCPT TO:<munged@supergenius.com >
Relaying not allowed - please use SMTP AUTH (in reply to RCPT TO
command)
I'm not relaying! Look:
[13:05][elvey@external ]$ dig +short supergenius.com NS
ns8.san.yahoo.com.
ns9.san.yahoo.com.
[13:05][elvey@external ]$ dig +short supergenius.com MX
20 mail1.wss.vip.scd.yahoo.com.

Also, PLEASE FIX:

http://www.rfc-ignorant.org/tools/loo...
http://www.rfc-ignorant.org/tools/loo...
etc.