[Dovecot] Invalid old index files

[Reinhard Vicinus]

Hi,

i'm in the process of evaluating dovecot. I have a rather big testing 
environment with four dovecot director frontend instances and four 
dovecot backend instances. Mailboxes are all in mdbox format and stored 
on nfs. Indexes are stored locally. dovecot nfs setup for high 
performance is used (mmap_disable = no, dotlock_use_excl = yes, 
mail_nfs_storage = yes, mail_nfs_index = no).

The remaining problem is, if i disable a backend server and the backend 
server which took over the connection already has some old index files, 
this index files aren't updated. If there aren't any index files all is 
fine and the index files are created anew. I can solve this by regularly 
deleting old index files via a cronjob. But i'm not sure if i made a 
configuration mistake and dovecot somehow can detect old index files 
automatically and invalidate them?

Thanks in advance
Reinhard