I know AOL has implemented some blacklists of mail servers originating from Dynamic IP address blocks, so that could be a problem if it thinks you or your ISP are on a Dynamic IP range and your users are trying to send emails to users @aol.com
http://postmaster.info.aol.com/
if this is the case then you will see aol's rejection messages in your qmail log.
another possibility is that if this is a dynamic ip, the isp providing the connectivity to the internet may be blocking outbound port 25. if this is the case you will have to use the isp's smtp server for all outgoing mail (using /var/qmail/control/smtproutes). i have done this type of filtering at the isp's where i worked- when the local spammers figured out that they couldn't get around the block, they went elsewhere.
it may also be that you're on one of the global blacklists. there's a tool at http://www.dnsstuff.com/ which can look up your ip in about a hundred different lists, within about fifteen seconds. just ignore things like blars and especially selwerd.cx (since they specifically tell you not to use their lists for blocking mail).
peace.
----------------------------------------------- | John Simpson - KG4ZOW - Programmer at Large | | <[EMAIL PROTECTED]> http://www.jms1.net/ | -----------------------------------------------
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