[Exim] "550 cannot route to sender address" from remote smtp…

hello,

i'm using exim in conjunction with Mailman and after some postings the
log file shows several of the following errors

** xxxx@??? R=dnslookup T=remote_smtp: SMTP error from remote
mailer\
after RCPT TO:<xxxx@???>: host mx00.schlund.de
[212.227.126.212]: 550 cannot route to sender address <su\
rprising-announcement-bounces@???>

how can i alleviate this? must i add an explicit mx record for
lists.surprising-enterprises.de? (surprising-enterprises.de has got
one, of course...)

thanks for your time,

tom
--
tom lazar <tom@???>