[Dovecot] Clients and dovecot-uidlist

[Timo Sirainen]

On Tue, 2009-07-28 at 19:30 +0200, Thomas Hummel wrote:
> Hello,
> 
> I'm trying to figure out what exactly (and why) are the consequences of a lost
> or removal of the dovecot-uidlist file on an IMAP client (Thunderbird for
> instance).

Just dovecot-uidlist, or also dovecot.index*? If you delete both,
UIDVALIDITY is changed. If you delete only dovecot-uidlist, it'll
probably preserve UIDVALIDITY and just give new UIDs to messages
(because next_uid is also stored in index file).

> I took for granted that it was that the client would download all messages
> again since it might be confused by some UID changes.  But I don't really see
> why (on the IMAP protocol level) and I don't know how to reproduce it.
> 
> My understanding is that 
> 
>   . dovecot-uidlist is not recreated until some client selects the mailbox
> 
>   . the client does something like :
> 
>      x UID fetch 1:* (FLAGS)
> 
>      to begin with anyway.
> 
> So I guess the problem does not occur when no new messages arrive on the mailbox
> since the same UIDs would be assigned to the same messages ?

Well, Dovecot reads the uidlist file lazily. If the index files still
exist and you don't try to open any mail or there are no new mails, then
uidlist's existence isn't checked and UIDs won't change.

> But can you show me some IMAP protocol command exchange that would illustrate 
> 
>   . when such a problem can occur
>   . how the client would detect that there has been some UID corruption
>   . how it would fix it 

Either the client notices that UIDVALIDITY changes on SELECT:

* OK [UIDVALIDITY 1248669921] UIDs valid

Or the UIDs change.
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