[exim] greylisting

I have grey listing running and it seems to work well stopping the bulk
of spam. But I had one chap complaining last week that some one was
emailing him and it was failing to get through.
A quick log check showed

2009-06-04 12:29:10 [76405] H=vscano-b2.ucl.ac.uk [128.40.105.157]:47833
I=[94.76.221.176]:25 F=<Egyptian@???> temporarily
rejected RCPT <Christine@???>: greylisted host
128.40.105.157

2009-06-04 12:29:10 [76405] H=vscano-b2.ucl.ac.uk [128.40.105.157]:47833
I=[94.76.221.176]:25 incomplete transaction (QUIT) from
<Egyptian@???>

2009-06-05 16:19:50 [48875] H=vscano-a2.ucl.ac.uk [144.82.100.153]:64384
I=[94.76.221.176]:25 F=<Egyptian@???> temporarily
rejected RCPT <Christine@???>: greylisted host
144.82.100.153

2009-06-05 16:19:50 [48875] H=vscano-a2.ucl.ac.uk [144.82.100.153]:64384
I=[94.76.221.176]:25 incomplete transaction (QUIT) from
<Egyptian@???>

So I guess there server just never retried after being grey listed at
least not from the same host. Other than not greylisting I take it
theres no way of avoiding the odd incident like this
There email got returned with a 550 unable to relay error. I am no
expert at this but I do try and get things right and avoid causing other
people problems.
I have since whitelisted them ( using postgrey by the way ) .

Thanks
Terry