Thanks for the replies.
Yes, it was on 2010-06-23 when the user deleted his emails between 2010-06-18 and 2010-06-22. Since there is no full backup from 2010-06-19, I need to use the previous one from 2010-06-18 (full-20100618.220013.785).
How can the restored mailbox contain emails newer than specified in the "Restore to a point in time" selection in the admin GUI? The restore operation seems to use the most recent backup regardless the time point I specify. The most recent backup, in this case, is not what I'm after. I tried the recovery using several timepoints prior to the date the deletion took place (2010-06-23).
Reindexing the restored mailbox did not make a difference.
It would be great to have "view mail" (or at least "view subjects/timestamps") feature for backups also.
There seems to be similar issues:
zmrestore point-in-time recovery not working