[Exim] Exim Rejecting messages randomly?

Hi List,
I'm having problems with mail getting rejected even thought it
shouldn't be (and I don't understand why). This is my ACL section of my
config file:

begin acl


acl_check_rcpt:

   accept  hosts          = :
   deny    local_parts    = ^.*[@%!/|]

  deny    senders        = \
                                            ${lookup mysql{SELECT sender
FROM deny_sender \
                                                  WHERE
'$sender_address' rlike sender} \
                                                  {$sender_address}}
           message        = We don't want mail from $sender_address,
your in our database.

   deny    hosts          = net-lsearch;/usr/exim/reject-hosts.txt : \
                            net24-lsearch;/usr/exim/reject-hosts.txt
           message        = Connection Denied for $sender_host_address

   accept  local_parts    = postmaster
           domains        = +local_domains

accept authenticated = *

   accept  domains        = +local_domains
           endpass
           message        = unknown user
           verify         = recipient

   accept  domains        = +relay_to_domains
           endpass
           message        = unrouteable address
       verify         = recipient

   accept  hosts          = +relay_from_hosts

   deny    message        = authentication required - relay not permitted

acl_check_data:

     accept

I have people send me email, and I receive it, and then the next day
they will send a message and it will be returned "Undeliverable" to
them. Then I will get random messages blocked for unknown reasons, and
they show up in the reject log like this:
2003-03-22 14:43:45 H=f4.law10.hotmail.com (hotmail.com) [64.4.15.4]
F=<email@???> rejected RCPT <me@???>: We don't want
mail from email@???, your in our database.
This person is definitely not in my database and emails SHOULD be
accepted.

Can someone help me out? I'm new to MTAs and just need a mail server
that looks up users in MySQL and delivers mail to them and doesn't
allow spamers to use my server. That is ALL I need. I spam filter on
the client side.
Thanks,
BJ Clark
bjclark@???