I think you may find it works (users can delete mail) if you put the Dovecot indexes on separate filesystem (preferably unquota'd). I haven't tested it, though. It seems to me that it is similar to the mailbox on a read-only filesystem case.
We have indexes on a seperate local filesystem without quota. It seems the problem is with creating the dovecot-uidlist file in $MAIL.
Cor
Ah, Maildir! In that case, you need to add :CONTROL=/some/other/filesystem/%u or whatever in the "default_mail_env" (or "location" for namespaces) setting. It's not documented, but was mentioned in an earlier thread about read-only mailboxes.
We have about 20 servers that customers can connect to. We try and put them on the same server every time, but we cant guarentee that since servers can crash or whatever.
All servers mount an NFS filesystem with a maildir based $MAIL. Indexes are on a local FS, since most of the time customers do actually connect to the same server, and indexes on NFS are a nightmare anyways.
The dovecot-uidlist seems like it cant be on a local FS. So we'd have to create a completely seperate NFS filesystem without quotas so all our 200.000 customers can have 1 file on it? :) Well, if we have to we have to..but it seems there could be a better solution..
Cor