[Dovecot] IMAP views - and things to make Outlook Express not suck so much

Timo Sirainen tss at iki.fi
Thu May 27 03:20:05 EEST 2004

On 27.5.2004, at 02:31, Geo Carncross wrote:

>> I've thought about something similiar before, but I've mostly just
>> thought about performance and complexity issues with it. Creating a
>> single view from many mailboxes could be slow without some special
>> indexing.
> It shouldn't be slower than performing the actions manually.

Sure, it's not, but clients aren't doing this manually now. Doing it in 
a simple way would be easy I guess, but I'm not sure if the performance 
would be good enough to be acceptable.. Especially if a view consists 
of tens of mailboxes. Each synchronization would require scanning 
through changes in all of them.

I had been thinking about making some global index about mailboxes and 
their states. So that by just reading one file would be able to tell 
what mailboxes have changed. With that kind of system it would work 
much better.

> The only
> "tricky" part would be the UIDL/ID matchups. If one is willing to
> implement 64-bit integers, or accept a 2^32 maximal limit on the number
> of messages accessible in a view, then the problem can be reduced to
> m=n*nfol+folnum where nfol is the number of subscribed folders, folnum
> is the relay counter, n is the original UIDL or ID number, and m is the
> resulting UIDL/ID passed to the client.

IMAP spec only allows using 32bit numbers, so UIDs and message counts 
can be max. 2^32-1. But I don't think the UID lookup is too difficult, 
I could just create a new index of uid => {original mailbox id, uid} 
mapping with simple increasing UIDs.
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