QMail Mail send issue

[CahitE]

Hello

My computer has an ip which is not listed in pbl or any spam list xxx.xxx.xxx.xxx
and 2 example client
1. yyy.yyy.yyy.yyy
2. zzz.zzz.zzz.zzz

this qmail servers ip address is mmm.mmm.mmm.mmm and also this seems perfect on mxtools.com and not listed any pbl or blacklist

Smtp auth. is activated and all the mail client settings same on all of us.

so how this happens ?

now when i want to send email over my mail client from this server everything is ok .

but 1. and 2. client if attempts to send mail got this error.
451 http://www.spamhaus.org/query/bl?ip=yyy.yyy.yyy.yyy
451 http://www.spamhaus.org/query/bl?ip=zzz.zzz.zzz.zzz