backup mails from alternate storage

Hi there!

It seems that # doveadm backup -v backup -fu $MUSER mdbox:"$BKPDIR/$MUSER/mdbox" doesn't backup all messages stored in alternate storage.

mail_location = mdbox:~/mdbox:ALT=/srv/mail/slow/vmail/%n/mdbox

I don't know how to debug this. The sizes of the mailboxes in the filesystems of user C are strange:

~/mdbox: # du -sm 2169

ALT: # du -sm 25252

backup: # du -sm 2658

This is with dovecot 2.2.9 on Ubuntu x86_64 14.04.2 LTS. Is this a bug or am I doing something wrong?

How can I test if messages stored in the alternate storage are successfully backed up?

Thanks Lars