Finding mail in tracking center

we have a client that is stating they occasionally are getting NDR messages and sent me over the information and thats definitely the case, when i goto tracking center i can see all the emails that are accepted/greylisted for them but i cannot see the one that was blocked. is there any additional information i can gain from tracking center? i have had a few people state they send mail and get NDR's back, and then when we goto look we cant seem to find the one that bounced back but see others from the same person that came through.

Thx
 
did you enable "include NDR`s"? if you cannot find what you are looking for, go through /var/log/syslog.