After all messages were deleted in mailbox (flagged '\Deleted' by IMAP and then expunged). After that each folder was checked to be 0 messages size.
Though, target mailbox was found on disk in /opt/zimbra/store and all deleted messages were found there. Furthermore those messages are not hardlinks as they are when multiple local recipients get a single message:
Is there any way to clear ZimbraStore from actually deleted messages?
zimbra@ms:~/store/0/29/msg/10> LC_ALL=en_US.UTF-8 stat 41628-37386.msg
Size: 2543 Blocks: 8 IO Block: 4096 regular file
Device: 803h/2051d Inode: 2843035 Links: 1
Access: (0640/-rw-r-----) Uid: ( 1001/ zimbra) Gid: ( 1000/ zimbra)
Access: 2011-04-20 16:33:26.000000000 +0400
Modify: 2011-04-19 16:13:18.000000000 +0400
Change: 2011-04-19 16:13:18.000000000 +0400