DAV:id does not retrieve mail.

Hi,

 For the s/w that I am developing, I require to fetch email from their DAV:id property. The scenario is 
something like this:
1. I fire a SEARCH query to get DAV:ids of mails satisfying some condition, say date=somedate.
2. I get back a set fo DAV:id s.
3. I construct a query again to fetch mails from these ids. But surprisingly only few mails are returned.
 Some mails are not returned inspite of having proper ids.
There is nothing wrong in the SEARCH query I am building, have checked and rechecked that.
I also tried using uid,permanenturl etc. But some mails just cannot be retrieved.

Could someone provide help.
Thanks,
Poorva