sync_client bails out after 3 MAILBOXES need upgrading to USER in one run

[David Carter]

On Tue, 12 Sep 2006, Wesley Craig wrote:

> On a related note, what was the problem with accepting the Cambridge 
> patches for delayed folder deletion?  I'm interested in working on 
> getting that or similar code accepted.  Now that we have delayed expunge 
> for messages, we continue to run tape backups only for the case where 
> users inadvertently delete folders.

Replication and delayed expunge were added by Ken (working as a 
contractor) back before he joined CMU. Replication was sponsored by 
Columbia. Delayed expunge was sponsored by Fastmail, but mostly as a 
performance enhancement. Unexpunge was just a nice side effect.

I believe that Ken implemented the delayed expunge from scratch. My 
original "two expunge expunge" code is rather more involved:

1) Users can access expunged mail and deleted mailboxes using magic
    mailbox hierarchies (.EXPUNGED/ and .DELETED/).

2) It hooks into the quota system to record the amount of expunged
    space in each quota root. Messages are automatically expired when
    global or per quota root limits are reached.

With hindsight (1) was a daft idea on my part. Our users struggle with the 
idea of multiple mailboxes in their account, let alone magic mailbox 
hierarchies. (2) is arguably useful if you don't have infinite storage on 
your IMAP backends. There are however lots of other spool partitions which 
can fill up under a determined denial of service attack.

Without (1) or (2), delayed mailbox deletion is really nothing more 
exciting than a RENAME operation to some part of the mailbox hierarchy 
without a quota root that only the system administrator can access.

-- 
David Carter                             Email: David.Carter at ucs.cam.ac.uk
University Computing Service,            Phone: (01223) 334502
New Museums Site, Pembroke Street,       Fax:   (01223) 334679
Cambridge UK. CB2 3QH.