Well, yes. He knows as much about you as can be revealed from your
email headers, i.e. the original source of the message. But if your
message is chained (as described above) to another remailer AND
ENCRYPTED with that remailer's key, then the first remailer (and
anyone snooping his traffic) cannot read your message. All they will
see is an encrypted message (with no subject line) that is heading to
some other remailer. Since your message must enter the remailer
network somewhere, that first remailer operator can always know where
the message is really coming from. It is for this reason that chained
messages should always be encrypted and not sent in the clear through
remailers that will accept clear text messages (Noisebox Remailer or
Xganon for example).
 
There is absolutely no security in sending an unencrypted chained
remailer message. Using remailers without encryption (whether it's PGP
or Mixmaster) is like a police officer choosing to leave his
bullet-proof vest at home in his closet!