[exim] ending up in spam folder

Hi a few of our customers are complaining when they send some mail it
never arrives with the recipient.
Checking the logs I can see the email has left our server successfully
for example


exigrep judithdavies63@??? /var/log/exim/mainlog
2009-09-04 14:47:46 1MjZ8g-0005px-2T H=bt830x85401.pndsl.co.uk (COMP3)
[81.174.167.166]:65005 I=[94.76.221.176]:25 Warning: Skipping spam scan;
message too large
2009-09-04 14:47:51 1MjZ8g-0005px-2T <= sales@???
H=bt830x85401.pndsl.co.uk (COMP3) [81.174.167.166]:65005
I=[94.76.221.176]:25 P=esmtpa A=plain_login:sales@???
S=195445
id=!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAAg8BI3qoT9UW6PkpPLkCQ8cKAAAAQAAAA8iWFTphX2Ue6vTL+vGSi/AEAAAAA@???
T="bcard proof" from <sales@???> for
judithdavies63@???
2009-09-04 14:47:52 1MjZ8g-0005px-2T => judithdavies63@???
F=<sales@???> R=outbound_throttled T=throttled_smtp
S=198097 H=mx2.mail.eu.yahoo.com [77.238.177.142] C="250 ok dirdel"
2009-09-04 14:47:52 1MjZ8g-0005px-2T Completed

A quick google shows me that 250 ok dirdel is a good sign and indicates
the message has been delivered.
So I assume the email has ended up in the junk folder. This also happens
to email to btinternet.com. This only applies to some email and not all.
The thing is a lot of end users have no clue about the spam folders and
settings so then complain they haven't had the email.
Is there any thing to be done to help avoid it

Thanks